CA1193993A - Reverse tab control system for typewriter - Google Patents

Abstract

REVERSE TAB CONTROL SYSTEM FOR TYPEWRITER
Abstract:
A typewriter has a Keyboard (12), including a Tab Set Key (22), a Tab Clear Key (24), and a Tab Actuating Key (26). Oper-ation of the tab set key stores stop positions of the Carrier (18) with respect to the typewriter's Platen (14). Shallow de-pression of the tab actuating key causes the carrier to move for-ward (right) to the next tab stop position. A first deep de-pression of the tab actuating key establishes a Reverse Tab Mode causing the carrier to move backward (left) to the nearest pre-ceding tab stop position and causing the platen to rotate (in-dex) so as to position the Printing Element (16) one line down on the paper, thereby to facilitate typing the next line of sin-gle column material without effecting a carrier return and for-ward movement of the carrier to the beginning of the column. Each subsequent shallow depression of the tab actuating key causes the carrier to move backward to the next preceding tab stop posi-tion without indexing, thereby to facilitate typing the next line of multiple column material without effecting a carrier return and forward movements of the carrier,. The Reverse Tab Mode can be ended by activating almost any other key, whereupon subsequent shallow depression of the tab key causes the carrier to move for-ward in normal fashion.

Description

01 Patent Applicat.ion of 02 Michael H. Smi-th 03 REVERSE. TAB CO~TROL SYSTEM

0~

07 Field of Invention 08 This invention relates to typewriters, particularly 09 to a typewriter having tabulation (tab) controls. More :10 particularly it relat~s to such a typewriter wherein reverse as 11 well as orward tab capabilities are provided.

~13 Description of Prior Art 14 Heretofore most typewriters contained tab controls for rapidly and automatically ad~usting -the relative posi~ons of :16 ~17 ~3~3 01 the printing mechanism (type bars or print head) and 02 the platen. In typewriters wit~ Eixed print heads 03 or -typebars, the platen was moved with respect -to 04 printing mechanism, and in typewri-ters with fixed 05 platens, the printing head ~a ball or a spoked and 06 riml ss "daisy" wheel) was moved wi~h respect to the 07 platen. For purposes of facilitating discussion, 08 the operation will be detailed with reference to the 09 latter type oE machine (the print head moves and the platen is Eixed), but the former type of machine 11 (print mechanism is fixed and platen moves) should 12 also be considered as an included method of tab 13 operation.
14 The tab feature is useful for enabling a typist to effect rapid and repetitive movements of 16 the printing mechanism to a plurality of different 17 horizontal positions along a line on the paper or 18 other recording web. In mechanical typewriters, the 19 tab stop positions were usually stored by positioning mechanical pawls to stop movement of the 21 platen at spaced horizontal locations, where 22 desired. In electronic typewriters, the output of 23 the keyboard consists of electronic signals which 24 are processed in an electroni.c data processing system within the typewriter to generate suitable 26 control signals for driving solenoids and step-or 27 servo-motors to cause the typing mechanism to print 28 selected characters and e~fect other operations;
29 here the tab stop positions usually were stored in an electronic memory and the carrier was moved to 31 the tab stop positions by means of a servomechanism 32 under control of the electronic data processing 33 system.
34 In most typewriters, the tab system was of the forward type only, i.e., the tab mechanism 36 was able to move the printing mechanism only to the 37 right with respect to the platan. This is ~3~33 01 disadvantageous in situations w~ere a typist must 02 type, for example, a single column of characters.
03 After typing a line of the column, to type the next 04 line the typist must return the print head to the 05 first character of the column. To do this, the 06 typist must choose one of two awkward alternatives.
07 The first alternative is to reset the left margin 08 control to the first character oE the column of 09 characters before typing the column. However this is an ~wkward operation and the original margin must 11 be located and restored when typing of the column is 12 completed. Alternatively, the typist can effect a 13 carrier return, causing the carrier to move all the 14 way to the left, and thereafter repeat tab until the carrier advances to the desired position; this is 16 also awkward and inefficient.
17 To avoid these drawbacks, typerwriters 18 recently have appeared with a reverse-tab 19 ~apability. In these typewriters, when a reverse-tab key was pressed, or when the regular tab 21 was actuated in a certain manner, different rom the 22 regular forward-tab method of actuation, the carrier 23 would move to the left with respect to the platen, 24 i~e., to the next tab stop at the left of its current position. The reverse-tab feature greatly 26 facilitated typing oE columnar material by ~7 eliminating the above drawbacks.

2~ As an added feature, some typewriters 2g have also provided an automatic line indexing or platen rotation feature upon opera-tion o the 31 reverse tab key. In this feature, when the reverse

3~ tab key was operated and the carrier moved to the 33 left with respect to the platen, the platen would 34 also index, i.e., rotate by an angle equivalent to one line space so as to cause the next line position 3~ on the paper to appear at the current typing 37 position. This made it even easier to type columnar D3~3 01 material since it eliminated the need for the typist 02 to manually advance to the next line space aEter a 03 reverse-tab operation.
04 However the above combination o~
05 indexing or line spacing with reverse tab was 06 disadvantageous when several columns of material 07 were being typed since this requires that the 08 carrier be moved to a second or even further-left 09 column ~rorn a curren-t typing posi-tion after each line is typed. The typist was not able to do this 11 easily by repetitively reverse tabbing because every 12 reverse-tab also caused an index; thus the correct 13 position Eor typing the next line would be lost upon 14 the second reverse-tab actuation. Thus in order to effect a reverse-tab movement to a second or 16 subsequent column, the typist had to repetitively 17 reverse tab to the desired column and thereafter 18 adjust the platen so that the correct line on the 19 paper was at the printing position. Alternatively, the typist could still effect a carrier return to 21 the left margin and then forward tab to the desired 22 column. However this did not take advan-tage o~ the 23 machine's reverse-tab capability and was also 2~ difficult and time consuming.
Accordingly, one object of the present 26 invention is to provide a typewriter with a 27 reverse-tab feature whereby reverse-tab operations 28 to the second or Eurther columns of typing material 29 to the left of the current posi-tion can be effected without adjusting the platen. Another object is to 31 provide such a typewriter with a more efficient 3~ reverse-tab operating sequence~ A further objec~ is 33 to provide an electronic typewriter with a novel 34 reverse-tab opera-ting feature.
Thus, according to one embodiment of the 3~ present invention, there is provided a tab control 37 system for a typewriter comprising a keyboard ~3~3 01 con-taining character keys; -type elements and a Q2 carrier therefor, mechanical striking apparatus 03 attached to the carrier and capable of striking the 04 type elements against a platen in accordance with 05 characters selected on the keyboard; the carrier, 06 the mechanical striking apparatus, and the type 07 elements being arranged to move axially with respect 08 to the platen, the carrier also being arranged to 09 move a predetermined distance .in a predetermined direction with the striking of any character of the 11 type element apparatus against the platen. ~le 12 keyboard includes a tab set apparatus for manually 13 presetting a plurality of tab stop positi.ons of the 14 carrier with respect to the p~aten, a tab clear apparatus for clearing any of -the plurality oE the 16 tab stop positions when set, and a tab actua-ting 17 apparatus responsive to a first kind of manual 18 actuation thereof for moving the carrier to any of 19 the plurality of preset tab stop positions. The system includes tab control apparatus for moving the 21 carrier from its present posi.tion to the closest 22 preset tab stop position in t:he predetermined 23 direction upon each rnanual actuation of the tab 24 actuating apparatus, the tab control apparatus also ~5 being arranged to move the carrier to the closest 26 predetermined tab position in a direction opposite ~7 to the predetermined direction and for rotating the 28 platen through a predeterminad angle so as to cause 29 any type-receiving medium positioned around the platen to move to a lower line position with respect 31 to the carrier, upon a second kind o manual 32 actuation of the tab actuating apparatus, and or 33 moving the carrier to the closest predetermined tab 34 position in the opposite direction and without rotating the platen, upon each manual actuation of 36 the tab control apparatus directly after the second 3l kind of manual actuation thereof.

~3~3 01 Fur-ther objects and advantages will 02 become apparent from a consideration of the ensuing 03 descrip~ion and the accompanying drawings.

05 Fig. 1 illustrates an electronic 06 typewriter according to the invention.
07 ~igs. 2A, 2B and 2C are diagrammatic 08 illustrations of a sequence of reverse tab 09 operations according to the invention.
Figs. 3A, 3B and 3C are a t~ree-part 11 flow chart showing the sequence of reverse-tab 12 operations according to the invention.
13 Fig. 4 is a block diagram of an 14 electronic system used in the typewriter of the invention.
16 FIG. l--ELECTRONIC TYPEWRITER
17 In Fig. 1, an Electronic Typewriter 10 18 according to the invention comprises the usual 1~ Keyboard 12, Platen 14, Print Wheel 16, and Movable Carrier 18 for Wheel 16. Pri.nt Wheel 16 is a common 21 spoked and rimless prin-t or "daisy" wheel: it has a 22 plurality of radial spokes or petals, each 23 containing a respective character of the keyboard.
24 When any character is typed, Wheel 16 is rotated so that the desired character petal is upright and then 26 a han~er (not shown) strikes such petal over an 27 inked or carbonnsd ribbon 20 onto a paper or other 28 wri-ting medium (not shown) which is fed over Platen 29 14.
Keyboard 12 contains the usual character 31 and control function keys, some of which are 32 indicated, and also contains the following keys of 33 particular interest: A Tab Set Key 22, a Tab Clear 34 Key 24, and a Tab ~ctuating (Tab) Key 26. Tab Clear Key 24 and Tab Key 26 are each depressible to either 36 a shallow position or a deep position for purposes 37 described subsequently. Typewriter 10 also includes 38 - 6 ~

01 a Control C:ircuit 28 which controls the Eunctions 02 and operations o Typewriter 10 in response to 03 actuation of character and control keys on Keyboard 04 12. Principally, Circuit 28 con-trols the operation 05 o Print ~heel 16, Platen 14, and Carrier 18.
06 More specifically, when a key on 07 Keyboard 12 representing a selected character is 08 depressed, a unique electronic signal representing 09 that key will be coupled to Control Circuit 28 which will in turn generate appropriate signals to cause 11 Print Wheel 16 to rotate so that a petal thereof 12 with the selected character is upright. Circuit 28 13 will also cause ~he hammer to strike that petal 14 against Platen 14 via Print Ribbon 20 so as to imprint the character on the paper and also move 16 Carrier 1~ to the right a distance equal to one 17 character pitch or one space, either before or after 18 the hammer operates, so that each subsequent 19 character will be typed one space to the ri~ht of the previous character.
21 FIG. 2 --REVERSE TAB OPERATION
22 Prior to describing the reverse tab 23 operation according to the invention, the forward 24 and prior-art reverse tab mocles of operation will be described in order to facilit:ate an understanding of 26 the inventive reverse tab operation.
27 Forward Tab 28 Referr:ing to Fig. 2A, assume that a 29 typist desired to t~pe a pluralit~ of columns on a paper, such as columns 30 and 32 indicated. Each 31 column is composed of successive rows of four 32 numbers each for purposes of example. The typist 33 set the first tab stop by moving Carrier 18 to the 34 horizontal position indicated at "TSl" (Tab Stop 1) and thereafter depressed Tab Set Key 22. A tab stop 36 was thereupon set at this position. Then Carrier 18 37 was moved to position TS2, the position of the first 01 charac-ter in column 32. The typist again depressed 02 Tab Set Key 22, thereby setting a second tab stop at 03 this posit.ion. Thereafter to type columns 30 and Q~ 32, the typist first pressed Tab Key 26 to cause the 05 carrier to move immediately and continuously from 06 any position left of column 30 to TSl, the carrier 07 stop position for printiny the ~irst charac-ter in 08 column 30. After the characters oE -the first row of 09 column 30 were typed, the typist again depressed Tab Key 26 to effect an immediate and con-tinuous 11 movement of Carrier 18 to TS2, the carrier stop 12 position for printing the first character in column 13 32.
14 The typist -then pushed the carrier return key, causing the carrier to move to the left 16 margin, which would be somewhere to the left of 17 position TSl, and also causing the platen to rotate 18 one line space so as to move the paper up one line.
19 The carrier was now in posit:ion to print the second line of columns 30 and 32. The typist again 21 depressed Tab Key 26 to move Carrier 18 to position 22 TSl, typed the second row of column 30, pushed Tab 23 Key again to move ~he carrier to position TS2, and 2~ then typed the characters in the second row of column 32. The.reafter the carrier was in position 26 to print in the ~ext character space to the right of 27 the last character ("1") of the second row of column 28 32, as indicated by the next print position (NPP) 29 indicator arrow 3~.
Prior Art Reverse Tab 31 If the typist were typing only a single 32 column, such as column 32, and the typewriter had 33 the prior-art reverse-tab-wi-th-index capability, the 34 typist was able to return the carrier to position TS2 and move the paper to the next line, as 36 ind.icated by path 33 in Fig. 2B, by either 37 depressing Tab Key 26 to a deep position (D) rather r ~3~3~3 01 than the usual shallow position (S~, or by actuating 02 a separate reverse tab key (not shown). Carrier 18 03 automatically moved backward continuously or 04 repeatedly backspaced to the next tab stop position 05 (TS2), and Platen 14 rotated one line (or several 06 lines if line spacing was so set), so that the print 07 posi-tion indica-tor moved to the left and down (line 08 36), to a position one lin~ under the first 09 character in the second row of column 32. Thus a third row of characters (not shown) could be typed 11 in column 32 without returning Carrier 18 to the 12 left margin and then forward tabbing one or more 13 times in order to move the carrier to position TS~
14 and one line below the last line typed.
However, if the typist were typing two 16 or mora columns, it was not possible, using the 17 prior-art reverse tab with index feature, to move 18 the carrier easily to the first character position 19 in the third row of first colurnn 30 since each subsequent reverse-tab operation would cause the 21 platen to index, so that -the print posi-tion 22 indicator would move to the fourth line position 23 (not shown) of column 30, thus requiring additional 2~ adjustments of the platen, or non-use of the reverse-tab feature when plural columns were being 26 typed.
27 Reverse Tab According to Invention 2~ As indicated in Fig. 2C at 35, if Tab 29 Key 26 is shallow depressed after the first deep depression thereo, the carrier will still rnove 31 leftward to the next left tab stop position TSl but 32 Platen 14 will not rotate. Thus the next print 33 position indicator 3~ will be in the correct 34 position to type the next row in column 30--i.e., one line under the first character in the second row 36 as shown. Hence, a typist could effect proper 37 reverse movements of the carrier very easily when 38 _ 9 _ ~:~~3~3 01 typing two columns by merely depressing Tab Key 26 02 -twice, the first depression being a deep depression, 03 tnereby moving Carrier 18 back to TSl and one line 04 down. If rnore than two columns are being typed, the 05 typist need merely depress Tab Key 26 a sufficient 06 number o additional times to reach the first column 07 being typed. The correct line and tab stop will 08 automatically be reached at any column withou-t the 09 need to effect a carrier return or rotate the platen in a separate operation.
11 The reverse tab moves have been 12 described in the foregoing paragraphs and 13 illustrated in Figs. 2B and 2C (by broken lines 36 14 and 38) as occurring directly upon a deep depression of Tab Key 26. However, in actuality, in a current 16 commercial embodiment oE the invention, any 17 depression of Tab Key 26 (shallow or deep) will 18 cause a forward tab move (if possible) which begins 19 immediately. If the depression of Key 26 is a deep one, after completing the forward tab move the 21 reverse tab moves described and illustrated will be 22 executed, i.e., the carrier will rnove directly back 23 to and through its posi-tion at start oE the forward 24 move. The overall results b~eing the same, the forward tab move and the corresponding return part 26 of the reverse tab moves have not been illustrated 27 in Figs. 2B and 2C in order to simplify the drawing.
28 To review, according to the invention a 29 deep depression of Tab Key 2~ will effect a movement of Carrier 18 ending at the next preceding tab stop 31 position (to the left), coupled with a rotation of 32 Platen 14 to the next line. ~ach subsequent shallow 33 depresion of Tab Key 26 will move Carrier 18 to the 34 next left tab position, without rotating the platen. (Subse~uent deep depressions of Tab Key 26 will cause Carrier 18 to move two tab stops to the 37 left, without a platen rotation. This operation is 01 not described infra for purposes of facilitation of 02 explanation.) 03 The normal mode of operation upon a 04 shallow depression of Tab Key 26 is a forward 05 (righ-tward) movement of the carrier to -the next tab 06 stop. This normal mGde can be restored (af-ter any 07 reverse movemen-t d~le to a deep depression of Tab Key 08 26) by operating any character key, the space bar, 09 or almost any other function key.
FIGS. 3A and 3B--FLOW CHART
, ll Figs. 3A and 3B depict the various 12 operations which occur within Control Circuit 28 to 13 effect the reverse tab mode of operation. The 14 various blocks within Figs. 3A and 3B depict individual operations which occur within Control 16 Circuit 28 and the order of progression of the 17 blocks depicts the sequence of these operations, in 18 accordance with well-known flow chart usage.
19 Contro:L Circuit 28 includes a microprocessor which, in accordance with the usual prac-tice, makes 21 continuous repetitive checks or interrogations of 22 various conditions in the machine and, depending 23 upon the state of such conditions, initiates or 24 ~kips appropriate ~ubroutines. The flow chart illustrates operations relevant to a subroutine 26 initia~ed when Circuit 28 detects that T~b Key 26 27 (Fig7 l) has been depressed.
2~ Fig. 3A--First Pass--Reverse Tab Key Entry 29 rrhe reverse tab mode is ini-tiated when Key 26 is deeply depressed. Two things thereupon 31 occur to effect a Reverse Tab Key Entry, as will now 3~ be discussed.
33 Deep depression of Key 26 causes a Key 34 Waiting Flag and Repeat Terminal Flag to be set.
These Elags correspond to binary cells in a memory 36 array or Status RAM 400 of Fig. 4 (described infra) 37 which indicate th~ status of various condi-tions or 3~393 01 components o~ the machine. Depression of any key on 02 Keyboard 12 causes the Key Waiting Flag to be set 03 directly by a signal on an output line 403, 04 indicating depression of a key (generally) on 05 Keyboard 12. Also, information corresponding to -the 06 iden-tity of the key depressed is provided at the 07 output of a keyboard Encoder or ROM 402 of Fig. 4 08 (described infra and forming part c)f a keyboard 09 Input Interface 401). Deep depression o Tab Key 26 moves a common bail 404 (Fig. 4), activating a ll mechanical coupling 406 which will in turn close a 12 single-pole-single-throw momentary switch 408. This 13 will ground and activate a Repeat Terminal input 14 lead 409 connected directly to a Repeat Terminal stage or flag in Status RAM 400 which is immediately 16 set, as a result. Normally the Repeat Terminal 17 input lead of RAM 400 is biased a-t a positive 18 voltage (non-activating) by Positive Source 410 and 19 Resistor 412. The Repeat Terminal input is used since it is a convenient method of effecting two 21 modes of operation (forward and reverse tab) with a 22 single Tab Key 26.
23 Box 44 Prior to describing the first operation, 24 it will be noted here that the above-mentioned flags are periodically checked or interrogated, part of a 26 rou-tine identified by a circular (connector) box 44, 27 labeled "Next Key Routine." Normally, Control 28 Circuit 28 is in this idling routine in which 29 interrogations of various ~lags or conditions in S-tatus RAM 400 are made. These will not ~e listed 31 here except insofar as relevant. After completing 32 any operation, the machine returns to its idling 33 routine so that Box 44 represents a significant 34 point in the flow chart.
Box 46 In its idling routine, Control Circuit -36 28 checks the Key Waiting Flag in RAM 400, as 37 indicated by diamond (decision) Box 46. Since the ~3~3~

01 Key Wai~ing Flag has been set, as described above, 02 the Yes output oE Box 46 will be followed.
03 Box 48 Next, itl response to the presence of the 04 Key Waiting Flay, a data number (code) representing 05 depression of Tab Key 26 and provided at the output 06 oE ROM 402, will be read and stored in a 07 First-In-First-Out (FIFO) Register which is Register 08 A in a Data Storage RAM 414, described inra. The 09 Key Waiting Flag will be cleared at the time of read out.
11 Box 50 I'o indicate that FIFO Register 414A is 12 occupied, a FIFO-Empty Flag in Status RAM 400 is 13 cleared, as shown by Box 50.
14 Box 52 Next, as indicated by this Box 52, the FIFO-Emp-ty stage of Status RAM 400 will be 16 interrogated. Since this stage was just cleared in 17 the operation of Box 50, the Mo output of Box 52 18 will be followed.
19 Box 54 Si.nce testing of the FIFO-Empty Flag has ~0 shown tha-t there is at least one Key (code) stored 21 in the FIFO (Box 52), the ne~t key in the FIFO, 22 regardless of its identity, will be transferred to a 23 ~ew Key Regis-ter 414I; the oldest and each 24 succeeding Key code will be successively ~ransferred, identified, and processed. Thus, in 26 its turn, the Tab Key data code will be transferred 27 from FIFO Register 414A, via an Accumulator 416, to 28 New Key Register 414I, as indicated in Box 54.
2g Also, a Repeat Elag in Status RAM 400 will be cleared if set. The Repeat flag differs from the 31 Repeat Terminal Flag which was set by deep 32 depression of Tab Key 26, and is used to cause the 33 machine to perform ~he Repeat function. The Repeat 34 Terminal Flag merely indicates that the Repeat Terminal of RAM 400 has been activated, i.e., Switch 36 408 has been closed.
37 Box 56 Next a determination is made in Box 56 , .. . ..

~3~33 01 as to whether the data transferred to New Key 02 Register 414I represents the Tab Key. The 03 determina~ion in Bo~ 56 is made to determine if the 04 reverse tab mode should be cleared if the tab key 05 code is not present in New Key Register 414I, as 06 more fully discussed below.
07 Box 58 Next, as indicated in Box 58, a two-part 08 FIFO-pointer Register 414K having a first part 414Kl 09 controlling the order of information readout rom FIFO Register 414A, is updated to account -for the 11 transfer that occurred in Box 54. Another part of 12 the FIFO-pointer register 414K2 controls the 13 position of Register 414A at which input information 14 i5 stored. The address information in these two parts of Register A14K controls the state of the 16 FIFO-Empty Flag in ~tatus RAM 400. IE that 17 information is identical, the FIFO is empty and the 18 ~IFO-Empty Flag is set, but is cleared upon a 19 subsequent key-entry. Thus, as part of ~ox 58 the pointer contents are compared in known fashion and 21 -the FIFO-Empty Flag updated accordingly.
22 Box 60 Other preliminary operations, not 23 relevant to the Reverse Tab operation, are made 24 after Box 58, where the flow chart route for the actual Tab routine begins, as indicated generally by ~6 the Key Decode Connector Box 60 at the bottom of 27 Fig. 3A, Part I and at -the top of Fig. 3B, Part II
28 of the Flow Chart. The Key Decode includes 29 ssgregation of function codes in known fashion.
Box 61 The next operation and the first of 31 Fig. 3B, indicated in this bo~, is one of the 32 routi.ne checks or interrogations performed by 33 Circuit 28. This operation is a decision which 34 determines whether the Key Code in New Key Register 414I is a non-print key. If not, this indicates 36 that the Key Code represents a printable character, 37 so -that the No output is followed and the printable ~3~3 01 Key is processed, as indicated in predefined process 02 Box 61A. Since the Tab Key is a non-printable or 03 "func-tion" Key, the Yes output is :EolLowed to Box 04 62. (In actuality, the decision of Box 61 05 determines whether the Key Code is greater than 91 06 since all printable Key codes have values less than 07 92 and all function Key codes have values greater 08 than 91.) 09 Box 62 The operation indicated in this box, is also one of the routine interrogations performed by 11 Circuit 28. This operation is a decision which 12 determines whether a function Key code found to be 13 in the New Key Register 414I is the Tab Key code.
14 If not, the No output of Box 62 will be followed and, as indicated by Box 6~, further tests to 16 iden-tify and process the function code are 17 performed, but are not relevant here. If the key to 18 be processed is the Tab ~ey, the Yes output of Box 19 62 will be followed to Box 66 Box 66 In this box, Circuit 28 determines 21 whether the left margin setting (a stored count of a 22 number of spaces from the lefl end of Platen 1~, 23 which count is initially preset automatically or 24 otherwise programmed by the typist) is greater than the carrier's present position, i.e., is the number 26 of spaces from the left end of Platen 14 to the left 27 margin greater than the number of spaces from the 28 left end to the present position of Carrier 18? If 29 the left margin setting is greater than the carrier present posit.ion, the carrier is outside the usual 31 text area--in other words, to the left of the left 32 margin--and the Yes output of Box 66 will be 33 followed, but if the carrier is to the right of the 3~ left margin, the No output of Box 66 will be followed.
36 Box 68 Assuming the carrier is to the let of _ 37 the left margin so that the ~es output of Bo~ 68 is ~3~3 01 followed, the next operation, illustrated by Box 68, 02 is to set a Carrier Desired Posi-tion Register 414F
03 to the stored value for the left margin position.
04 ThereaEter, as illustrated by Box 70, the machine 05 makes a forward (rightward) move to the left margin.
06 When the position o Carrier 18 is to 07 the left oE the left margin, actuation of Tab Key 26 08 will cause Carrier 18 to move rightward to the left 09 margin, and no reverse move will -take place, even if Tab Key 26 is deeply depressed, and any tab s~ops 11 set to the left of the left margin being ignored.
12 This mode of operation is provided as it would be an 13 undesirable and probably mistaken mode of operatio~
14 to try to move the carrier to any tab stops which might be set ou-tside the left margin.
16 Box 44 Bis After the forward move to the left 17 margin (Box 70) the machine returns to its normal 18 idling procedure or Next Key Routine, as illustrated 19 by connector Box 44 of Fig. 3B, which connects to Box 44 o Fig. 3A. The machine will Eollow the flow 21 chart and ultimately reach connector Box 130 of 22 Fig. 3C, in which a user error indication i9 23 provided. This sequence will not be detailed.
24 Box 72 If the decision in Box 66 is ~o, i.e., the carrier is not to the left of the let margin, 26 the next step i9 to sat a Margin Release Flay, as 27 indicated in Box 72. Setting a Margin Release Flag 28 involves setting a regist~r (not shown) to a certain 29 state which will enable forward tab moves to be made to and to the right o the right margin without 31 operating the margin release key.
32 Box 74 The next step, illustrated by Box 74, is 33 to determine whether the Reverse Tab Mode Flag has 34 been set. The Reverse Tab Mode Flag, also in Sta~us ~M 400, is set after the reverse tab mode had been 36 en~ered. If Tab Key 26 has been deep-depressed for 37 the first -time, the machine will not yet be in the . .

3~33 01 Reverse Tab mode so that the Reverse Tab Mode Flag 02 will not have been set and the No output of Bo~ 74 03 will be followed. However, if the machine has 04 previously entered the Reverse Tab mocle, the flag 05 will be in the set state and the Yes output oE Box 06 74 will be followed.
07 B 76 Since the Reverse Tab Mode Flag has not 08 yet been set, the No outpu-t of Box 74 is followed.
09 The next operation is a decision (Box 76) to see i the Repeat Flag has been set. Since only the Repeat ll Terminal Flag has been set thus Ear (Box 42), the No 12 output of Box 76 will be followed to Box 77.
13 Box 77 A forward tab move is then executed, as 14 indicated in Box 77, to the next tab stop to ~he right of the carrier's present posi-tion, or if there 16 i5 no such tab stop, the carrier will proceed to the 17 right margin. When the forward tab move is 18 completed, the machine has cornpleted its first pass l9 of the flow chart and continues to the Next Key Routine, as indicated by Box 44, which connects with 21 that same Box at the top oE Fig. 3A.
22 Fig. 3A--Second Pass--Repeat Flag Tests 23 Box 46 Bis Returning to Fig. 3A, where the 24 operation~ continue at the output of Box 44, the second pass through Fig. 3 Part I of the flow chart 26 is made, this time ~or performing various Repeat 27 Flag tests. A decision is again made in Box 46 as 28 to whether the Key Waiting Flag has been set. The 29 Key Waiting Flag is no longer set, since the Tab Key code awaiting entry was delivered from ROM 402 to 31 the FIFO (Box 48) at which time the Key Waiting Flag 32 was reset, as mentioned earlier; and providing the 33 typist has not depressed further keys, as will be 34 assumed for purposes of this description; so that the ~o output of Box 46 is followed to Box 52.
36 Box 52 Bis Again the FIFO-Empty Flag is checked in -37 Box 52, but this time the decision will be Yes, 3~33 01 since the tab key was transferred from -the FIFO in 02 Box 54 and -the empty flag was set in Box 58.
03 Box 78 Next, as indicate~d in this box, the 04 RPpea-t Terminal Flag in S-tatus RAM 400 is checked.
05 This flag was a]ready set as previously described in 06 the introductory remarks concerning the Flow, so 07 that the Yes output of Box 78 will be followed.
08 Note that this flag can only be cleared upon the 09 typist's release of the deep depressed Tab Key 26.
Box 80 The Repeat-In Flag is then checked.
11 This flag is set when the Repeat Terminal Flag has 12 been recognized and processed. Since this has not 13 yet been done, the decision in Box 80 will be No.
14 Box 82 A short delay (20ms) is provided in Box 82 to allow termination o-F any transients resulting 16 Erom deep depression oE Tab Key 26 and activation of 17 Switch 408, thereby to prevent false triggering.
18 Box 84 The FIFO-Empty Flag is next checked.
19 Since this f].ag is now set, as explained in the second discussion o~ Box 52 above, the Yes output is 21 followed.
22 Box 8 A check is again made of the Repeat 23 Terminal Flag. As explained above in the discussion 24 of Box 78, this flag is still set, so the Yes output is followed. If not set after the delay of Box 82, 26 this indicates the Repeat Terminal Flag seen in Box 27 78 was caused by an unwanted transient signal.
28 _ox 87 Next, the Repeat Flag (indicating the 29 machine should repeat the key in the ~ew Key Register) i~ set and the Repeat-In Flag (indicating 31 that the Repeat Terrninal Flag has been recognized~
32 is also set.
33 The sequence then proceeds agai.n through 34 connector Box 60 to Part II of the flow chart in Fig. 3B through Box 62 tYes), Box 66 (No), Box 72 36 (No) to Box 76 again.
37 Fig. 3B--Reverse Tab Entry ~3~3 01 Box 76 Bis The Repeat Flag has just been set in Box 02 87, so that the Yes output of Box 76 is followed on 03 the second pass through the box, whereupon actual 04 entry oE the Reverse Tab Mode is begun.
05 Box 88 The next step (Box 88) is to set a Line 06 Feed Flag and a Reverse Tab Mode Flag (bo~h also in 07 Status RAM 400) to indicate that upon the nex-t 08 execution of a mechanical operation, a line feed 09 (rotation) of Platen 14 and a reverse tab opera~ion should both be efected.
11 Returning to Box 74, if the Reverse Tab 12 Mode Flag were already set at the ~ime of the 13 decision in Box 74, the Yes ou~put of Box 74 would 14 be followed to the output of Box 88. This path is taken when the machine is already in the Reverse Tab 16 mode, in which case the decision of Box 76 and the 17 flag setting of Box 88 would not be appropriate.
18 The Reverse Tab Flag would already be set and the 19 Line Feed Flag should not he set since a line eed is desired only upon the Eirst reverse tab move and 21 according to one main aspect of ~he invention is 22 omitted thereafter.
23 Box 90 Next, the Repeat Flag (in Status RAM
24 400) is cleared, as indicated in this box, in order to prevent continuously repeated reverse tab 26 operations. Also the Margin Release Flag, set in 27 Box 72, will be cleared to prevent any moves through 28 the margins on subsequent key inputs.
29 Locating Tab Stop Box 92 Next, as illustrated in Box 92, a Tab 31 Pointer Register, which is present as Register H of 32 Data Storage R~M 414 tFig. 4), is set to address the 33 highest address cell in a Tab Stop Register 34 (Register G of RAM 414). The Tab Stop Register stores the positions or "Stops" along Platen 14 to 36 which Carrier 18 will advance on -tab moves. Tab 37 Stop Register 414G has, in the present embodiment, 01 sixteen seven-bit cells for storing previously set 02 tab stops (from left to right) along the printing 03 line. In the operation of Box 92, the tab pointer 04 is set to address the highest-address cell in 05 Register 414G, i.e., the cell w~ich would store the 06 rightmost tab position i all sixteen possible tab 07 stops were se-t.
08 More particularly, when tab settings are 09 made, they are supplied to the sixteen cells of Tab Stop Register 414G in order of their numbered space 11 positions along Platen 14, with ~he leftmost tab 12 stop setting being supplied to the cell with ~he 13 lowest address in Register 414G, the next left tab 14 stop setting to the cell with the next higher address, and so on. If less than the sixteen 16 possible tab stops are set, the cells without a tab 17 stop will automatically be supplied with a reading 18 of 127, which is at least one higher than the 19 maximum tab stop setting position possible for a machine set to 12-pitch (12 charact~rs per 21 horizontal inch) and having a writing line of 10.5 22 inches. In Box 92, Tab Point:er Register 414H is set 23 to address t~e cell with the highest possible 24 address as a first step in locating the closest tab stop to the left of Carrier ].8. The tab stop cells 26 are addressed and checked in reverse order, ~rom 27 highest address to lowest, in oraer to locate such 28 closest-left tab stop.
29 Box 94 Next, as indicated, a decision is made to determine whether the carrier's presen-t position 31 (stored in a Carrier Present Position Register 414D) 32 equals the setting in the cell addressed by -~he Tab 33 Pointer Register. If the decision is Yes, the 34 currently-addressed c811, which is the maximum-address cell of Tab Stop Register 414D, 36 contains a valid carrier stop setting ~less than 127 37 for a machine set to 12-pitch), indicating that all . `'.

01 sixteen possible carrier stop settings have been 02 made, and the carrier is presently at that stop 03 setting, which is the rightmost tab stop. If the 04 d~cision is No, there was either no tab setting in 05 the maximum-address cell, i.eO, the maximum-address 06 cell i5 set to an impossible carrier position (127), 07 or the carrier is to either side of the set-ting in 08 the maximum address cell.
09 Box 96 Assuming the No output o~ Box 94 is followed, i.e., the carrier is to either side o the ll set-ting of the maximum-address cell or there is no 12 tab stop in the maximum-address cell, a decision 13 will next be made (Box 961 to determine whether -the 14 carrier's present position is less than the setting in the cell addressed by the Tab Pointer Register, 16 which i5 still the maximum-address cell. If the 17 decision is No, the carrier is to the right of 18 position in the address cell, which cell has been 19 set with a valid carrier position. Therefore, as indicaked by connection Box 98, the closest tab stop 21 to the left o~ the carrier has been ound.
22 If the decision in Box 96 is Yes, i.e., 23 the carrier's present position is less than the 24 position in the cell addressed by the Tab Pointer Register, this indicates that the carrier is 26 somewhere to the let of the maximum tab stop 27 setting in the Tab Set Register.
28 Box 100 Assuming the carrier is to the lef~ of 29 the setting in the cell addressed by ~he Tab Pointer Register (Yes rom Box 98), or if the carrier's 31 present position is equal to the position in the 32 cell addressed (Yes from Box 94), next a decision 33 will be made (Box 100) to determine whe-ther Tab 34 Pointer is addressing the minimum-address cell of the Tab Stop Register. In the present round the Tab 36 Pointer could not be at such minimum-address cell 37 since it has just been set to he maximum-address 3~ - 21 -g3~
01 cell (Box 92), so that No output of Box 100 must be 02 followed.
03 Bvx 102 When the No output of Box 100 is 04 followed, as indicated in Box 102, Tab Pointer 05 Register will be set -to address the next-lower 06 address cell of the Tab Stop Register. In other 07 words, the Tab Pointer Register is decremented to 08 address the next lower possible tab setting 09 position.
Box 94 Bis Next, -the output of Box 102 (on the left 11 side thereof) is followed back up to decision Box 12 94, where again a determination is made as to 13 whether the setting in the Carrier Present Position 14 Register is equal to setting of the cell in the Tab Stop Register currently addressed by the Tab Pointer 16 Register, which in the present round is the cell 17 with the next-to-highest address.
18 Box 96 Bis If the decision in Box 94 is No, a 19 decision is again rnade (Box 96) to see whether the set-ting in the Carrier Present Position Register is 21 less than that in the addressed cell. If the 22 decision in Box 96 is No, the setting in the cell 23 addre~sed by the Tab Po:inter Register is now 24 established to be the closest tab position left of the carrier, as indicated by Box 98.
26 Box 100 Bis Returning to Box 94, if the setting in 27 the Carrier Present Position Register equals the 28 setting in the cell addressed by -the Tab Pointer 29 Register, the Yes decision from Box 94 will be followed, and a decision will be made ~Box 100) to 31 determine whether th~ Tab Pointer Register is 32 addressing the minimum address cell of the Tab Set 33 Register. If so, the Yes output of Box 100 will now 34 be followed, indicating that all possible tab set positions have been surveyed and (Box 104) no tab to 36 ~he left of the carrier was found.
37 Box 102 Bis If the decision in Box 100 is ~o, i.e., 3~ - 22 -3~3 01 the tab pointer is not addressing the minimum 02 position of the Tab Se-t Register, the tab pointer is 03 again decremented (Box 102~ and the decisions in Box 04 94, 96 and possibly Box 100 are made, as before.
05 Tab Stop Found 06 Box 106 If a tab stop position to the left of 07 the carier was found (Box 98), a connection is made 08 (Box 99) to Fig. 3C where the next operation (Box 09 106) is to set a Carrier Desired Position Register (414F) to the value in the cell addressed by Tab 11 Pointer Register 414H. This is done in order to 12 move the carrier to the setting in the cell 13 addressed by Tab Stop Register 414G.
14 Box 108 Next, a decision is made ~Box 108) to determine whether the setting in the Carrier Desired 16 Position Register is greater than that of the left 17 margin. If so, this indicates that the Carrier 18 Desired Position is inside the lef~ margin, 19 whereupon the Yes output of Box 108 will be followed. If the Carrier Desired Position Register 21 is not greater than the left margin, the ~o output 22 of Box 108 will be ollowed, indicating that the 23 desired tab stop is outside or. to the left of the 24 left margin. In this case it would not be desirable to move t~e carrier further to the left.
26 Box 110 If the desired tab stop is outside the 27 left margin, i.e., the No output of Box 108 is 28 followed, next ~Box 110) the Carrier Desired 29 Position Register is set to the left margin setting so that the carrier will go to the left margin at 31 the next move.
32 Box 112 After the Carrier Desired Position 33 Register is set to the left margin (Box 110), or if 34 the Carrier Desired Position Register's setting is greater than the left margin (Yes from Box 108), 36 Accumulator 416 is set (Box 112) to the difference 37 between the setting of the Carrier Present Position 3~3 01 Register and that of the Carrier Desired Posi-tion 02 Register in order to indicate the number of spaces 03 by which the carrier must move to reach the desired 04 position.
05 Box 114 Thereafter, a Print Wheel Step Count 06 Register 414J (Fig. 4) is set to zero to prevent the 07 carrier Erom making a single letter space movement, 08 which it might do if a number were set in Register 09 414J.
10 Box 116 The Carrier Space Count Register is then 11 set to the "number" or "value" in Accumulator 416.
12 This .is in preparation for movement of the ~arrier, 13 which moves according to the setting in Carrier 14 Space Count Register 414C.
Next (also Box 116), the Carrier 16 Direction Flag (in Status RAM 400) is cleared. This 17 flag is normally set to move the carrier to the 18 right and the clearing thereof is in preparation for 19 a left or reverse move.
Box 118 Next, the value in Carrier Present 21 Position Register 414D is set to the value in 22 Carrier Desired Position Register 414F. This is 23 done so that the Carrier Present Position Register 24 will store the carrier's actual position after the tab move is completed and so that the carrier will 26 return to this desired position if a machine or 27 motor error occurs during carr.ier movement.
28 Box 119 A timer (not shown) is preferably used 29 to control (among other events, if desired) a Linefeed Motor (not shown) for rotating Platen 14.
31 In this box, the timer is reset.
32 Box 120 In this box, a decision is made next as 33 to whether the Linefeed Flag (in RAM 400) has been 34 set. If Tab Key 26 has been deeply depressed-~i.e., if the first reverse tab movement is being made--the 36 Linefeed and Raverse Tab Mode Flags will have been 37 set in Bo~ 88. If the Reverse Tab Mode Flag was 3L~L~3~3 01 already set ~Yes from Box 74)- i.e., a second or 02 subsequent reverse tab move is being made--then 03 Boxes 76 and B8 will be bypassed and consequently 04 the Linefeed Flag will not have been set via Box 88.
05 Box 122 If the first reverse tab movement is 06 being made, the Linefeed and Reverse Tab Flags will 07 have been set in Box 88 so that a Yes decision will 08 be made in Box 120 and (Box 122) rotation of the 0~ platen one line ahead, in accordance with ~he invention, is started. Substantially a~ the same 11 time, the carrier will stArt its move (Box 124) in 12 the left direction by -the value in the Carrier Space 13 Count Register--iOe., to the next left tab stop.
14 If a second or subsequent reverse tab movement is being made, the Reverse Tab Flag will 16 have been set so that a Yes decision in Box 74 will 17 cause ~ox 88 to be bypassed and the Lineeed Flag, 18 which is cleared at the end of the Eirst rever~e tab 19 movement (see Box 126 below) will still be clear, so that a ~o decision will be made in Box 1200 21 Accordingly~ Box 122 is bypas~ed and only the 22 carrier move (Box 124) to the next tab stop position 23 at left is performed. The reverse move is then 24 completed.
While a relatively large number ~f 26 decisions and operations have been described as 27 occurring between the Forward Tab Move (Box 77) and 28 the Reverse Tab Move (Box 122), in actualityl due to 29 the high clock rate of the machine, the Reverse Tab Move appears to occur substantially immediately 31 after the Forward Tab Move.
32 Box 126 After completing the above rnoves, then, 33 as shown in this box and in accordance with the 34 invention, the Linefeed Flag, which was originally set in Box 88 upon entry into the Reverse Tab Mode, 36 is cleared in order that subsequent shallow 37 depressions of the tab key will eEfect a reverse tab ~3~3 01 move without a linefeed, as discussed supra.
02 Box 44 Bis As seen Erom Box 126 the sequence 03 returns to Box 44, the Next Key Routine, which 04 includes Box 54 where the oldest Key Code in F'IF0 05 Register 414A is transferred to New Key Register 06 414I, via the Accumulator. IE the tab Key has been 07 depressed twice in succession, the Key transferred 08 will be the tab key but, if not, the key will be a 09 character, space or other key. Discussion of these circumstances will be undertaken subsequently.
11 Tab Stop ~ot Found 12 Box 128 Returning to Box 104 (Fig. 3B3, if no 13 tab to the left of the carriex was found, a 14 connection is made (Box 105) to Fig. 3C where a decision is then made ~Box 128) as to whe-ther the 16 carrier is presently at the left margin, i.e., is 17 the setting in the Carrier Present Position Register 18 414D equal to the setting in the Left Margin 19 Register 414E? If so, the carrier cannot be moved to any tab stop position and the machine proceeds 21 (Box 130) to the user error subroutine in which 22 error lights (not shown) are flashed.
23 Box 132 If the carrier present position is not 24 equal to the left margin position, the No decision output oE Box 128 will be followed and the Carrier 26 Desired Position Register will be set (Box 132) to 27 the value in the Left Margin Position Register in 2~ order to move the carrier to the left margin.
29 Thereafter, the actual carrier movement is completed as indicated in Boxes 112 to 126.
31 Box 44 Bis Whether or not a tab stop -to the left of 32 the carrier is found, the Reverse Tab Movement 33 procedure ends at Box 126, as seen above. From 34 there the output is again followed back to Box 44 of Fig. 3A, at which point the machine resumes its 36 normal idling or Next KQY Routine.
37 Fig. 3A---Tab Key Held Deep Depressed 01 If the typis~ holds the Tab Key deeply 02 depressed during and after -the reverse tab move, the 03 machine will not make any further reverse tab moves 04 after the first one because of the sequence which is 0S now followed in Fig. 3A.
06 Boxes 46 and 52 .The Key Waiting Flag is not set _.
07 since it was cleared upon delivery of the waiting 08 Tab Key Code from ROM 402 to the FIFO, as explained 09 supra, and the typist has not depressed a key other than Tab Key 26. (Such action would be an error, as 11 it would override the desired reverse tab 12 operation.) Thus the No output of Box 46 is 13 followed. The FIFO-Empty Flag is set, so the Yes 14 output of Box 52 i5 also followed.
Boxes 78 and 80 The Repeat Terminal Flag is set 16 since it is assumed that the Tab Key is being held 17 deep-depressed. In Flag was set in Box ~7 and was 18 never cleared so the Yes output of Box 80 is also 19 followed.
BOX 133 The Repeat Flag is tested in Box 133.
__ 21 Since that flag was cleared in the reverse tab entry 22 (BOX 90), the No output of Box 132 is followed, back 23 to the idling routine (BGX 44). ThUs no further 24 reverse tab moves will occur, even if Key 26 is held 25 deep depressed.
26 _ g 3A~-Tab Key Released 27 _ox 134 When the tab key is released, the 28 machine will follow the No output of Box 46, the Yes 29 output of Box 52, the No output of Box 78 (the Repeat Terminal is no longer made active since 31 Switch 408 will now be open~ to Box 134 where the 32 Yes output is followed since the Repeat-In Flag, 33 which was sei in Box 87, was never cleared. Th~
34 routine will proceed through Box 82, follow the Yes output of Box 84 (the FIFO is empty) and the No 36 output of Box 86 ~a flag check operation identical 37 to that in Box 7i3) to Box 136.

01 _ox 136 In this box, the Repeat and Repeat-In 02 Flags are cleared and the machine returns to its 03 idling routine.
04 _g 3A--Tab Ke~ Pressed Again 05 After the irst reverse tab move, which 06 was accompanied by a linefeed, if the Tab Key 26 is 07 pressed again but ~his time only shallowly, the 08 machine will pursue the following rou-te through the 09 flow chart to effect a second reverse tab movement (path 38 of Fig. 2C): Ye~ ~rom Box 46, Box 48, Box 11 50, No from Box 52, Box 54, Yes from Box 56, Box 58 12 to Box 60 in Fig. 3B, Yes Erom Box 62, No Erom Box 13 66, Box 72, Yes from Box 74 (the Reverse Tab Mode 14 Flag, set in Box 88, was never cleared), through Boxes 90, to 98 and 106, 120, as described above.
16 In Box 120, as stated, the ~o output will be 17 followed since the Linefeed Flag was cleared in Box 18 126 on the first reverse tab movement, the result 19 being that Carrier 18 will be moved (Box 124), but not Platen 14, in accordance with the invention.
21 Fig. 3A--Non-Tab Key Pressed 22 The Reverse Tab Mode can be exited by 23 depressing a character key or almost any function 24 key other than Tab. When this is done, the machine will proceed along the "First Pass" route o~ Fig. 3A
26 to Box 56, the non-tab key being detected and the No 27 output then followed to Box 138, where the Reverse 28 Tab Mode Flag is cleared, thereby exiting the 29 Reverse Tab Mode. The path then proceeds -to Box 58 for up-date of the F~FO pointers before passing 31 onward to Key Decode (connector Box 60) w~ere the 32 non-Tab Key is identified and processed in normal 33 fashion, -the details not being relevant here.
34 FIG. 4 - BLOCK DIAGRAM OF HARDWARE
-A block diagram oE the electronic system 36 of Control Circuit 28 to effect the operations in 37 the flow chart of Fig. 3A and 3B is shown in Fig.

.r~.
~ , ' 0l 4. In practice, all the components in the control 02 circui-t may be formed within a single integrated 03 circuit or microprocessor chip~ Appropriate 04 ampliEication of output signals for driving the 05 printed and other mechanisms will also be provided.
06 In order to facilitate understanding, simplify the 07 explanation, and avoid undue length, only the 08 typewriter components relating to the inven-tion and 09 their ancillary components are detailed. Also only the most important inputs and outputs, data 11 interconnections, and address interconnections o 12 the invention components are shown in the block 13 diagram of Fig. 4. Omitted are details of the other 1~ typewriter components and various ancillary circuits and lines to and from the components of the 16 invention s.ince their implementation is either shown 17 in the above-referenced applica~ions or is readily 18 practicable by those skilled in the microprocessor 19 or logic circuit design arts, given -the flow chart of Figs. 3A and 3B together with the block diagram 21 of Fig. 4.
22 As indicated by t:he legend at right of 23 Fig. 4, address busses (which generally carry 24 information designating an "address" or location in a memory matrix) are desi~nal:ed by double lines 26 inter-connected by zig-zag llnes, and data busses 27 (which generally carry substantive information) are 28 indicated by double lines interconnected by parallel 29 slant lines. The num~ers in parentheses adjacen-t various busses--e.g., "(7)"---indicate the number o 31 lines or conductors in the bus. As is well known in 32 the art, a seven-conductor bus can transmit data 33 words or by-tes oE seven bits, and since each bit 34 represents a digit in radix 2--i.e., the presence (O~E bit) or absence (ZERO bit) of successive powers 36 of two in a summed progression from 2 to 26--such 37 a bus can transmit decimal numbers (radix 10~ up to 3~ - 29 -~3~q33 01 127.
02 A Keyboard Interface Unit 401 receives 03 inputs directly from ~Ceyboard 12, these include 04 inputs designating se1ected characters, index 05 (linefeed), a backspace input, a correct input, a 06 tab set (Key 22), a tab clear ~Key 24), a tab 07 activate (Key 26), margin controls, space, and 08 return, as indicated.
09 Preferably Keyboard 12 employs an 10 acoustic sanding means and Interface 401 includes 11 ROM 402 (mentioned earlier) and appropriate 12 circui.try which converts the resultant acoustic 13 inputs into appropriate data signals in a parallel 14 readout format suitable -for directly driving Print Wheel 16 and other m~chanical outputs, as detailed 16 in the above-mentioned applications. A control 17 signal indicating the availability of these data 18 signals i8 sent directly to RAM 400 vi.a line 403 (as 19 ~tated earlier). A standard keyboard employing electrical switches throughout can be used instead;
21 in this case Keyboard Inter~ace Unit 401 would be a 22 more common variety.
23 Status RAM 400, already mentioned, is a 24 register having sixty-four single-bit storage cells;
it stores various flags indicating the sta-tus of an 26 ongoing operation or any instruction for the machine 27 to follow upon its usual interrogation rounds. RAM
28 400 is periodically polled or interrogated as part 29 of the normal idling routine of the system in order to determine if any flags are set, and if set (or 31 not set), the system will execute an appropriate 32 subroutine. E.g., when Repeat Switch 408 is closed, 33 an appropriate stage of RAM 400 will become set 34 thereby to indicate that the machine should repeat an operation or enter a special subroutine, such as 36 reverse tab. RAM 400 is polled via an address input 37 from an address bus 418 which selects a desired 01 stage in RAM 400. RAM 400 thereupon supplies a 02 single output indicating the s-tatus of the stage 03 selected.
04 RAM 400 receives eleven control tnputs.
05 Four come directly from keys or switches on ~n 06 adjacent Keyboard 12, one (pitch selection) comes 07 from a printed circuit board (not shown), one comes 08 from the print wheel to indicate a home position, 09 four come from motors (directly and indirectly) as feedback signals, and one (left end) comes from a 11 limit switch on the machine's frame. The inputs are 12 labelled and not all of these will be detailed since 13 they are well-known to those skilled in the art.
14 As stated with regard to the Repea-t Terminal input on lead 409 which is of most 16 interest, when Tab Key 26 is deeply depressed, the 17 voltage on l~ad 409 to ~AM 400 will become active.
18 In practice, the voltage on that lead is positive 19 when inactive and falls to a ground level when active, i.e., when Repeat Switch 408 is closed.
21 This is indicated in Fig. 4 by connection of lead 22 409 to positive voltage source 410 via resistor 23 412. The same circuit is associated with Tab Clear 24 Key 24; it also operates Switc-h 408 by a bail, which can be the same bail as Bail 404. When Tab Clear 26 Key 24 i5 shallow-depressed (Switch 408 still open), 27 any tab setting at the carrier's present position 28 will be cleared, and when Tab Clear Key 24 is 29 deep-depressed, all tab se-ttings will be cleared regardless of the carrier's position.
31 Reerring to the upper lefthand corner 32 of Fig. 4, a Dead Key and Hammer Energy Latch and 33 ROM 420 has 256 stages of three bits each. It 34 receives information from a data bus 422, specifically it receives processed key infor~ation 36 from a FIFO (first-in-Eirst-out) register 414A and 37 latches (stores) this key information. The stored ~3'~33 01 key information i6 read when needed to determine if 02 the key is a "dead key" (i.e,, the carrier does no-t 03 advance after printiny t~e key's character, such as 04 a letter which is to have an accent mark typed over 05 it) and also to determine which of four possible 06 hammar energies to use when printing the 07 character--e.g., less energy would be used to print 08 a character with a small area, such as a period 09 ("."), than a character with a large area, such as a "W".
11 Arithmetic Logic Unit (ALU) 424 receives 12 information from data bus 422 and Accumulator 416, 13 already mentioned. It performs simple arithmetic 14 and logical (comparison) opera-tions, such as the AND
and OR functions, addition, subtraction, division, 16 etc. when these operations are required by the 17 system. For example, using ALU 424, the existing 18 number of spaces from the le:Ethancl margin a~ which 19 Carrier 18 is presently positioned can be added with a nurnber representing an incremental movement of 21 Carrier 18 in order to provicle a sum equal to the 22 new position of Carrier 18. ALU 424 also makes 23 appropriate computations to control the carrier 24 return position and computati.ons to calculate the shortest possible path and corresponding direction 26 of rotation when Print Wheel 16 is to be rotated 27 from one character to another character. ALU 424 28 supplies a data output to Accumulator 416 and a 29 control output to an Instruction Disable Unit (IDU) 426. The control output to IDU 426 can be either a 31 carry, greater than, or "equal" ou-tput to indicate 32 the result of a comparison in ALU 424.
33 ~ccumulator 416 is a temporary storage 34 register which, e.g., holds information being worked on by ALU 424, in well-lcnown fashion. As indicated, 36 Accumulator 416 receives and supplies information to 37 data bus 422 and ALU 424.

~ ~ 3~6~

01 Instruction D.isable Uni-t (ID~) 426 02 receives inputs from ALU 424 and Status RAM 400 and, 03 according to the input received, can supply a "skip"
04 inpu-t -to an Instruction Decoder 428 which causes a 05 Program Counter 430 to increment one extra count.
06 I.E., when ALV 424 supplies a comparison ("carry,"
07 "greater than" or "equal") output, or when Status 08 RAM 400 supplies an output--indicating a set (true) 09 or non-set (false) flag--IDU 426 can supply a skip 1~ signal to Decoder 428 in accoxdance with the state 11 of the particular output which will in turn cause 12 the next sequential instruc-tion to be skipped. Thus 13 IDU 128 can effect a skip or not as to the result of 14 a comparison or a flag test.
Data S~orage RAM 414, already mentioned, 16 has registers which hold variable data, i.e., it has 17 a FIFO (first-in-first-out) Register (A) for storing 18 characters corresponding to keys actuated but not 19 yet printed, a Correction Register (B) for storing the last group (ten in one embodiment) of keys 21 actually typed, a Carrier Space Count Register (C~, 22 a Carrier Present Position Register (D), Left and 23 Right Margin Registers (E), a. Carrier Desired 24 Position Register (F), a Tab S-top Register (G) which, as mentioned, has sixt.een four-bit cells for 26 storing tab stop settings, a Tab Pointer Register 27 (H), a ~ew Key Register (I), a Print Wheel 5tep 28 Count Register (J), FIFO Pointers tKl, K2) and other 29 registers not relevant to the present invention.
RAM 414 can be considered as having sixty-four 31 locations, each capable of holding seven bits of 32 informa~ion. Some of Registers 414A to 414K
33 correspond to respective locations, while others, 34 such as Correction Register (~) and Tab Stop Register tG), require several locations. In 36 well-known fashion, the information in any selecte~
37 register in RAM 414 can be read out by providing an 38 33 ~

01 appropriate address input on an Address Bus 418 and 02 applying an appropriate and well-known con-trol or 03 read input (not shown) from Decoder 428 to enable 04 the data to be read into or out o~ RAM 414 via Data 05 Bus 422 leading from its right side.
06 Address Latch 432 receivcs an address 07 from a current instruction being e~ecuted and holds 08 it so that such address can be supplied -to RAM 414 09 (via a Decoder 434) for enough time for data to be read out or written at the appropriate point in RAM
11 414, in well-known fashion. Latch 432 supplies the 12 six bits of the address to Decoder 434.
13 Decoder 434 operates to select or enable 14 one address in RAM 414 or RAM 400 (one o-f sixty-Eour stages) at which to write in or read out 16 information.
17 Storage Register 436 is used for 18 subroutines; it stores the information word ~rom 19 Program Counter 430 to which to return after the subroutine is completed. Re~lster 436 has three 21 stages of eleven bit.s each.
22 Program Counter 430 causes the system to 23 operate in accordance with the instructions on the 24 flow chart by supplying appropriate address to a Program ROM 438. Program Counter 430 tends to 26 supply sequential addresses, but works in 27 association with Storage Register 436 such that when 28 the machine is ready to call any subroutine, the 29 current address or count in Program Counter 430 will be stored in Register 436. After the subroutine is 31 completed, the stored address in Register 436 will 32 be returned to Counter 430 so that it can cause the 33 machine to resume its regular routine of operation.
34 Also, as stated in the discussion of IDU
(Instruction Disable Unit~ 426, an address in 36 Counter 430 can be skipped if IDU 426 causes 37 Instruction Decoder 428 to increment Program Counter 3~3~

01 430 a second time. Counter 430 also can be set to 02 any address by an unconditional branch instruction:
03 this will cause eleven address bits in an 04 Instruc~ion Latch 440 to be passed around on Address 05 Bus 442 through Storage Register 436 and then -to 06 Counter 430, where they will be latched.
07 Program ROM 438 contai~s the actual 08 program of -the system, i.e., in response to 09 sequential or other address inputs from Counter 430, it delivers appropriate instruction words (each 11 having an address or data and operation code) which 12 cause the machine to operate in accordance with the 13 flow chart of Fig. 3. For example, Program ROM 438 14 selects appropriate stages of Status RAM 400 in order to determine whether cer-tain flags are set at 16 appropriate times. Program ROM 438 contains an 17 Input Decoder and Drivers and Output Drivers, as 18 indicated. ROM 438 has 1536 stages of thirteen bits 19 each.
Instruction La~ch 440 holds the 21 instruction word of Program ROM 438 curren-tly being 22 executed, in well-known Eashion.
23 Instruction Decoder 428 receives -the 24 output of Latch 440. Decoder 428 is a ROM which controls the actual physical operation of the 26 machine by gating information in and out of various 27 units of the machine via the bus lines, under 28 control of Program ROM 438. ~s stated previously, 29 Decoder 428 can also cause an instruction to be skipped in response to the skip signal from IDU
31 426. The output or control lines of Decoder 428 are 32 merely indicated by arrows in Fig. 4 because their 33 connections are well-known and including them would 34 make the figure less easy to follow.
Bufer 444 is a tri-state device, i,e., 36 it can supply a bi.nary ONE output, a binary ZERO
37 output, or provide a high input-to-output '',~" ' 01 impedance. It connects address bus 442 on its left 02 side to -the outputs oE the machine and also connects 03 data into R~M 414 via data bus 422.
04 Clock and Power On Reset Generator 446 05 provides the master clock pulses for the machine and 06 also resets all the registers oE the machine (power 07 on reset) when the machine is ~irst turned on. For 08 purposes of simplification and ease of illustration, 09 the various outputs of Generator 446, which lead to most of the blocks in the figure, are not shown, but 11 the connections are well-known to those skilled in 12 the art.
13 Also not shown is a timer uni-t for 14 providing various time delays, when required by operation of the machine. Further, a power supply 16 and biasing network for energizing the various 17 circuits is not shown either.
18 Miscellaneous Output Register and 19 Drivers 448 provides outputs to drive various ~unctions of the mac'nine, suc~ as a print hammer, a 21 warning tone to indicate the set margin is being 22 approached, a linefeed to ro-t:ate Pla~en 14, a print 23 or correct ribbon lift control, detents for Print 24 Wheel 16 and Carrier 18 which hold these elements in a fixed po~ition when not in use, and various 26 indicator lights as noted.
27 Carrie~ Decoder and Driver Register 450 28 drives the motor which controls the horizontal 29 position o Carrier 18, by interpreting the instruction bits supplied on Data Bus 422 from ROM
31 438 to select appropriate windings for causing the 32 carrier to move either to the right or to the left, 33 in increments. When a tab move is called, data will 34 be supplied to Register 450 so as to cause the carrier motor (not shown) to move to the next tab 36 stop at either left or right, in accordance with the 37 depth oE depression of Tab Key 26.
38 ~ 36 -~3~"33 01 Print Wheel Decoder and Driver Register 02 452 controls the motor which rotates Printing 03 Element 16, thereby to select appropriate characters 04 to be typed. When a character is called, data will 05 be supplied to Register 452 so as -to cause the prin-t 06 wheel motor to ro-tate wheel 16 to the selected 07 character.
08 FIGS. 3 & 4 - OPERATION
09 The system o Fig. 4 implements the flow chart operations of Figs. 3A and 3B in -the following 11 manner:
12 When Tab Key 26 on Keyboard 12 is 13 depressed deeply, the tab input is coded--as by an 14 acoustic signal to the previously-mentioned circuitry (not shown) to generate the Tab Key code 16 in ROM 402--and, due to actuation of Switch 408 by 17 common bail 404, the Repeat Terminal lead 403 to lB Status RAM 400 goes active (to ground)~ When the 19 code is available, a signal is sent on line 403, and immediately sets the Keyboard Waiting Flay of Status 21 RAM 400. Likewise, the active state of Repeat 22 Terminal lead 409 immediately sets the Repeat 23 ~erminal Flag in Status RAM 400, as stated 24 previously.
As part of its routine interrogation 26 rounds, thP machine wi~l then test selected flag~ in 27 RAM 400--e.g., the Key Wai-ting Flag, and since thi~
28 was set by a key actuation on Keyboard 12, the 29 corresponding code from ROM 402 will be entered into FIFO Register 414A. The Xey codes in FIFO Register 31 414A will be processed--in order of their entry into 32 FIFO 414A--by trans-Eerring t'ne key codes Erom 33 Register 414A to New Key Register 414I and then to 34 Accumulator 416. When the tab key code is transerrPd in its turn to New Key Register 414I and 36 Accumulator 416, that code will be identi-Eied as a 37 function code and the value in Accumulator 416 then ~ 5~3 01 compared for equality with a series of function key 02 codes obtained from Program ROM 438 in a 03 pre~selected sequence. When the value :in 04 Accumulator 416 is eventually compared with the tab 05 code (binary code for decimal 115), equality will 06 exist (Yes output oE Box 62), and ALU 424 will 07 provide a "true" signal on its "equal" output line 08 tFig. 4) ko IDU 426. As a result, in accordance 09 wi-th previous description, instead of causing a skip, the output of IDU 426 will cause Instruction 11 Decoder 428 to advance Program Counter 430 to 12 addres~ the next sequential instruction in ROM 438, 13 which is an unconditional branch. The machine will 14 thus jump to the tab subroutine, as explained in more detail below and as derined in the subsequent 16 blocks of Fig. 3B.
17 Note that the above-mentioned tests o 18 the value in Accumulator 416 (tab code~ against 19 other function codes ~ave rise to "false" signals on the "equal" output line of AI.U 424 and, under 21 control of IDU 426 and Decoder 428, these generated 22 skip inputs to Program Counter 430 which caused each 23 associated unconditional branch to be bypassed in 24 the fashion previously described and known in the art.
26 More particularly, the above-mentioned 27 no-skip causes a "branch-to-tab" instruction. This 28 is accomplished by transf rring that instruction 29 which is at the next sequential address in Program ROM 438 to Instruction Latch 440. This will, in 31 turn, cause the coumt in Program Counter 430 to be 32 abruptly changed ("jumped"~ to the par~icular 33 address for the start of the tab subroutine (Box 34 6~). This is done by passing the eleven least signiicant bits in Latch 440 twhich latched the 36 unconditional branch instruction, including the 37 particular address indicated by these bits) through 01 Storage Register 43~, and into Program Counter 430.
02 Counter 430 now addresses the initial portion of the 03 tab program stored in Program ROM 438--i.e., that 04 portion associated with Box 66. Execution oE thls 05 portion of the program proceeds as follows:
06 The first decision to be made (Box 663 07 is to determine whether the left margin setting (in OJ3 a Left and Right Margin Register 414E) is greater 09 than the setting in the Carrier Present Position Register 414D. This test is accomplished by a count 11 comparison in ALU 42A. If, as is usual, the left 12 margin reading is not greater than the carrier 13 present position, ALU 424 will provide a "false"
14 input to IDU 426, which will then supply a skip input to Decoder 428~ Program Counter 430 then will 16 be caused to increment by one extra count so -that it 17 addresses the next sequential instruction in ProcJram 18 ROM 43S (the instruction ater the unconditional 19 branch). In response to -the new instruc-t.ion, the six least significant bits in Latch 440 are put on-to 21 Data Bus 422 via Buffer 444 and these bits are hei!d 22 in Aadress Latch 432. This group of bits or address 23 in Latch 432 is then decoded by Decoder 428 which 24 selects one of the locations in Status RAM 400. As indica~ed in Box 72, the addr.ess selected is that o-f 26 the Margin Release Flag and that stage is thereupon 27 set in known fashion to permit direct tabbing to any 28 tab stops at righ~ of the right margin.
29,-~ Before continuing with the normal routine, note that if the left margin setting is 31 greater than the carrier present position, ALU 416 32 will detect a "greater than" and send a "true" input 33 to IDU 426, which last will not cause a skip inpu~
34 to be sent to Decoder 428. Accordingly, -the very next instruction of the sequence, an unconditional 36 branch, will be executed. As a result, Program 37 Counter 430 will be set--via Storage Register 436, 13L~93r9~3 01 as explained previously--to the address in Latch 440 02 corresponding to the start of -the program section 03 associated with Box 68. Execution of this portion 04 of the program then proceeds, i.e., the Carrier 05 Desired Postion Register will be set to the value 06 stored in the left ma.rgin .register, and a forward 07 move oE the carrier t.o the leEt margin executed ~Box 08 70) in steps not rele,vant here.
09 ~len (Box 74~, a check is made to see iE
the Reverse rrab Mode Flag is set. The address of 11 this Elag in R~M 400 as selected by ~he six least 12 significant bits of t.he instruction in Latch 440, 13 which are transferredl-to Latch 432 via Bu:Efer 444 14 and Data Box 422 and decoded by Decoder 428, in the fashion described pre!viously with respect to the 16 Margin Release Flag (Box 72)~ If the flag is set, 17 the output of Status R~M 400 will be true, and an 18 appropriate input wil.l be sent IDU 426 which will in 19 turn not provide a sk:ip input to Instruction Decoder 428 so that the next instruction will not be 21 skipped, but will be addressed and fetched in 22 sequence by Program C'ounter 430O This will be an 23 unconditional branch instruction, which will cause 24 Program Counter 430 t:o be set to the address of the 2S start of the program section associated with Box 90 26 (the next operation, since the Yes output of Box 74 27 bypassed Boxas 76 ancl 88). For this purpose, the 28 eleven leas-t ~igni~ic!ant bits in Instruction Latch 29 440 (which latched the unconditional branch instruction) are agai.n passed through Storage 31 Register 436 and loacled into Program Counter 430.
32 The Program Counter now addresses the start of the 33 reverse subroutine (i.n ROM 438) and execution of 34 this por-tion of the program accordingly proceeds.
If, on the other hand, the output of 36 Status ~ 400 is fa].se--i.e., the Reverse Tab Mode 37 Flag is not set~--IDU 426 will provide a skip input ~ ~3~t~ ~

01 to Instruction Decoder 428 which will cause (as 02 above) ~rogram Counter 430 to increment by one extra 03 count. The Program Counter then addresses the 04 instruction in Program ~OM 438 sequentially 05 followi~g the next or unconditional branch 06 instruction. The unconditional brarlch instruc-tion 07 has, thereore, been skipped. E~ecution of the 08 skip on alse flag instruction is completed at 09 this point.
The Repe,~t Flag is then checked (Box 76) 11 in the same fashion as the Reverse Tab Mode Flag was 12 checked (Box 74). I:E the Repeat Flag is clear, as 13 it will bs initially because of the sequence of -the 14 signals obtained upon deep depression of Tab Key 26, a forward tab move operation is ini-tiated (Box 77 ), 16 but if the Repeat Flag has been set, the operations 17 in Box 88 will proceed, under the aforedescribed 18 steps in wh.ich a skip input :is not generated and ~he 19 very next instructiom in the tab program sequence is followed, giving rise to a jump in the setting oE
21 Program Counter 430.
22 ~he program proceeds as indicated with 23 operations in rectangular boxes being carried on 24 according to straight-forward sequential program commands (generally, and excepting jumps for 26 returning to the main program path) and decisions in 27 diamond boxes being 3electively implemented by 28 presence or absence of a skip input from IDU 428 29 under control of the output of ALU 424 or an input from Status ~AM 400.
31 Moving down to Boxes 120, 122 and 124, 32 these depict the first reverse actions as a resul-t 33 o the reverse tab subroutine, which actions depend 34 on the state of the :Linefeed flag. As seen in Box 120, if the flag is set (true, or yes ), the 36 response is a let move routine including a linefeed 37 (Box 122) because the platen is to index one line.

~t33~93 01 This response does not require branching because 02 only a single step is required: an appropriate 03 command is sent to Miscellaneous Output Register and 04 Drivers ~48 which activates, for example, the 05 line~feed drive motor (not shown~. Activation is for 06 a fixed time (the timer having been reset in Box 07 119, as previously mentioned~ to operate properly a 08 cam mechanism (also not shown) such as the one 09 disclosed in the ~.S. Patent 4,365,90~ issued December 18, 1982, invented by Hans W. Mueller et 11 al, enti-tled "Linespacing Apparatus".
12 Since activation of the linefeed drive 13 motor is for a fixed time, completion of linefeed is 14 not required before proceeding, so with substantially negligible delay, the next sequential 16 instruction is fetched and it (together with others 17 following it) causes the carrier to be moved in the 18 left direction by the desired amount (Box 124 in 19 accordance with Box 116). Appropriate instructions are provided to Carrier Decoder and Driver Register 21 450 from Bu~fer 444 under control of Instruction 22 Decoder ROM 428. If the opexation of Box 122 is 23 bypassed (by virtue of a skip input of the type 24 described previously), the same carrier move is effected, but without the lime~eed, because the same 26 point in the program is reached in either case.
27 After the action in Box 126 (described 28 above) the reverse tab move will be complete!. Note 29 particularly that the! clearance (Box 126~ is effected in essentially the same sequence as the 31 setting of the Margin, Release Flag (Box 72) except 32 that a zero is writte!n in the cell of Status RAM 400 33 corresponding to the Linefeed Flag.
34 Although a complicated and relatively lengthy sequence of operations was described, due to 36 the high clock rate of operation of the electronic 37 system, these moves t:ake place very rapidly when Tab 38 - ~2 -01 Key 26 ls depressed or is deep-depressed.
02 While the above description contains 03 many specifities, ~hese should not be considered as 04 limited the scope of the invention since many 05 ramifications of the embodiment descxibed will be 06 apparent to those skilled in the art. For example, 07 in the reverse tab operation described, a first deep 08 depresslon of the reverse tab key causes a reverse 09 tab motlon plus a linefeed or index, and subsequent shallow depression oi- the reverse tab key causes a 11 reverse tab operation only. This mode of operation 12 can be lmplemen~ed mechanically in a non-electronic 13 typewriter by providing a linefeed upon a first 14 reverse tab operatiorl and by providing an approprlate mechanism to prevent linefeed upon 16 subsequent reverse tab operation~. The 17 "anti-llnefeed-upon-c;ubsequent-reverse-tabs"
18 mechanism would be c]eared upon opera-tion of any 19 character or space key. Also while the -tab and reverse tab operations were operated by a slngle Tab 21 Key 26, it will be apparent that a separate reverse 22 tab key can be provicled, in which case the reverse 23 tab key would have only two positions, i.e., off and 24 on; in the on po~ition the tab activate input to ROM
402 and the actuation of Repeat Switch 408 of Fig. 5 26 would occur. Many variation~; in ~he rules for 27 entering reverse tab, especially in association with 28 the margins, can be made within the scope o the 29 invention. Also, in lieu of making a forward tab move first, the machine can alternatively go 31 directly into the reverse -tab movement upon 32 activation of the reverse tab function, say by 33 introduction o sufficient delay to permit sensing 34 subsequent closure ol. Switch 408 during tab key depression, although this is not preferred because 36 of possibly noticeable delay accompanying -the more 37 frequently used forward tab moves. Accordingly it 3~'~3 01 is therefore desired that the true scope of the 02 inv~ntion be determined only according to the 03 appended claims and their legal equivalents.

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3~

38 - ~4 -

Claims (7)

1. The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
   
   l. A tab control system for a typewriter comprising a keyboard containing character keys; type elements and a carrier therefor; mechanical striking means attached to said carrier and capable of striking said type elements against a platen in accordance with characters selected on said keyboard, said carrier, said mechanical striking means, and said type elements being arranged to move axially with respect to said platen, said carrier also being arranged to move a predetermined distance in a predetermined direction with the striking of any character of said type element means against said platen, said keyboard having:
   (a) tab set means for manually presetting a plurality of tab stop positions of said carrier with respect to said platen, (b) tab clear means for manually clearing any of said plurality of said tab stop positions, when set, (c) tab actuating means responsive to a first kind of manual actuation thereof for moving said carrier to any of said plurality of preset tab stop positions, said system including tab control means for moving said carrier from its present position to the closest preset tab stop position in said predetermined direction upon each manual actuation of said tab actuating means, said tab control means also being arranged to move said carrier to the closest predetermined tab position in a direction opposite to said predetermined direction and for rotating said platen through a predetermined angle so as to cause any type-receiving medium positioned around said platen to move to a lower line position with respect to said carrier, upon a second kind of manual actuation of said tab actuating means, and for moving said carrier to the closest predetermined tab position in said opposite direction and without rotating said platen, upon each manual actuation of said tab control means directly after said second kind of manual actuation thereof.
2. 2. The tab control system of claim 1 wherein said tab actuating means comprises a single tab key on said keyboard, said tab control means being normally arranged to actuate said move of said carrier in said predetermined direction upon a shallow depression of said tab key and said opposite movement of said carrier upon a deep depression of said tab key, said deep depression of said tab key being said second kind of manual actuation thereof, and wherein said tab control means is arranged to actuate said opposite movement of said carrier upon any shallow despression of said tab key thereof following any deep depression thereof.
3. 3. The tab control system of claim 2 wherein said tab actuating means is arranged to provide a first output from said keyboard upon a shallow depression of said tab key, and a combination of said first output and a second output from said keyboard upon a deep depression of said tab key.
4. 4. The tab control system of claim 3 wherein said second. output is a keyboard control function which actuates a function of said typewriter other than said tab function when said tab function is not. being operated.
5. 5. The tab control system of claim 1 further including margin limit setting controls on said typewriter for limiting the leftmost and rightmost positions of said carrier with respect to said platen provided no margin release operation has been effected, and further including means for preventing a leftward movement of said carrier with respect to said platen if said carrier is positioned to the left of the leftmost margin limit position.
6. 6. The tab control system of claim 1 wherein said typewriter comprises an electronic system responsive to outputs from said keyboard for generating control signals in accordance with keys actuated on said keyboard, said type element means, said carrier, and said mechanical striking means being responsive to said control signals for actuating operation thereof, said tab actuating means being arranged to provide a first electrical output upon shallow depression of a tab key on said keyboard and a combination of said first electrical output and a second electrical output upon deep depression of said tab key.
7. 7. The tab control system of claim 1 wherein said tab control means is arranged to move said carrier in said predetermined direction to said closest preset tab position upon any manual actuation of said tab actuating means of said first kind after a manual actuation of a key on said keyboard other than one of said tab means.