JP4497166B2 - Analog input switching circuit - Google Patents

Analog input switching circuit Download PDF

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JP4497166B2
JP4497166B2 JP2007050091A JP2007050091A JP4497166B2 JP 4497166 B2 JP4497166 B2 JP 4497166B2 JP 2007050091 A JP2007050091 A JP 2007050091A JP 2007050091 A JP2007050091 A JP 2007050091A JP 4497166 B2 JP4497166 B2 JP 4497166B2
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直行 和佐
剛 高島
康祥 北野
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Panasonic Corp
Panasonic Electric Works Co Ltd
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Matsushita Electric Works Ltd
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Description

本発明は、アナログ入力切換回路に関するものである。   The present invention relates to an analog input switching circuit.

従来、アナログ入力切換回路は例えばプログラマブルロジックコントローラ（ＰＬＣ）などに用いられ、外部接続端子から入力されるアナログ値に基づいて各種対象機器の制御（例えば温度やストローク幅、荷重範囲などの制御）を行う機能を有している。外部接続端子から入力されるアナログ値としては、例えば対象機器に基づく外部電圧や外部抵抗の抵抗値などがある。なお、外部抵抗としては、例えばサーミスタやボリューム（可変抵抗器、ポテンショメータ）などが用いられる。   Conventionally, an analog input switching circuit is used for a programmable logic controller (PLC), for example, and controls various target devices (for example, control of temperature, stroke width, load range, etc.) based on an analog value input from an external connection terminal. Has the function to perform. Examples of the analog value input from the external connection terminal include an external voltage based on the target device and a resistance value of an external resistor. As the external resistance, for example, a thermistor or a volume (variable resistor, potentiometer) is used.

このような機能を有する従来のアナログ入力切換回路の一例として、図５に示すようなものがある。図５に示す従来のアナログ入力切換回路８は、アナログ電圧が入力される第１のＡ／Ｄポート（アナログ／デジタル変換ポート）８００及び第２のＡ／Ｄポート８０１を有するマイコン８０と、マイコン８０の電源電圧Ｖｃｃと同等の電圧が印加される第１の外部接続端子８１と、第１のＡ／Ｄポート８００に接続される第２の外部接続端子８２と、第１の分圧抵抗８６を介して第２のＡ／Ｄポート８０１に接続される第３の外部接続端子８３と、グランドに接続される第４の外部接続端子８４及び第５の外部接続端子８５とを備えている。   An example of a conventional analog input switching circuit having such a function is shown in FIG. A conventional analog input switching circuit 8 shown in FIG. 5 includes a microcomputer 80 having a first A / D port (analog / digital conversion port) 800 and a second A / D port 801 to which an analog voltage is input, and a microcomputer The first external connection terminal 81 to which a voltage equivalent to the power supply voltage Vcc of 80 is applied, the second external connection terminal 82 connected to the first A / D port 800, and the first voltage dividing resistor 86 And a third external connection terminal 83 connected to the second A / D port 801, and a fourth external connection terminal 84 and a fifth external connection terminal 85 connected to the ground.

このような構成の従来のアナログ入力切換回路８は、最大電圧がマイコン８０の電源電圧Ｖｃｃ以上である外部電圧６の陽極が第３の外部接続端子８３に接続され、陰極が第４の外部接続端子８４に接続されると、第１の分圧抵抗８６と第２の分圧抵抗８７によって、第２のＡ／Ｄポート８０１に入力される電圧を電源電圧Ｖｃｃ以下とし、この電圧を用いてマイコン８０が対象機器（図示せず）を制御する。これに対して、外部抵抗７及び外部分圧抵抗７０による直列回路の一端が第１の外部接続端子８１に接続され、他端が第５の外部接続端子８５に接続され、外部抵抗７と外部分圧抵抗７０の間が第２の外部接続端子８２に接続されると、第２の外部接続端子８２からの電圧が第１のＡ／Ｄポート８００に入力され、この電圧を用いてマイコン８０が対象機器を制御する。   In the conventional analog input switching circuit 8 having such a configuration, the anode of the external voltage 6 whose maximum voltage is equal to or higher than the power supply voltage Vcc of the microcomputer 80 is connected to the third external connection terminal 83 and the cathode is the fourth external connection. When connected to the terminal 84, the voltage input to the second A / D port 801 is made lower than the power supply voltage Vcc by the first voltage dividing resistor 86 and the second voltage dividing resistor 87, and this voltage is used. The microcomputer 80 controls a target device (not shown). On the other hand, one end of the series circuit including the external resistor 7 and the external partial pressure resistor 70 is connected to the first external connection terminal 81, and the other end is connected to the fifth external connection terminal 85. When the space between the partial pressure resistors 70 is connected to the second external connection terminal 82, the voltage from the second external connection terminal 82 is input to the first A / D port 800, and the microcomputer 80 uses this voltage. Controls the target device.

また、上記とは別の従来のアナログ入力切換回路として、特許文献１には、分圧手段と２つのサーミスタとが直列に接続され、分圧手段と各サーミスタの間の電位をマイコンのＡ／Ｄポートに取り込む温度検出回路が開示されている。この特許文献１のマイコンは、外部電圧を測定する機能を有してはいないものの、２つのサーミスタの一方が分圧手段に接続されるように半導体スイッチの切り換えを行い、切り換えた後にＡ／Ｄポートに取り込んだ電位からサーミスタの抵抗値を算出し、算出した抵抗値から温度を検出することができる。
特開２００３−１２１２７０号公報（段落００１６〜００２３及び第３図） Further, as a conventional analog input switching circuit different from the above, in Patent Document 1, a voltage dividing means and two thermistors are connected in series, and the potential between the voltage dividing means and each thermistor is set to A / A of the microcomputer. A temperature detection circuit for taking in the D port is disclosed. Although the microcomputer disclosed in Patent Document 1 does not have a function of measuring an external voltage, the semiconductor switch is switched so that one of the two thermistors is connected to the voltage dividing means. The resistance value of the thermistor can be calculated from the potential taken into the port, and the temperature can be detected from the calculated resistance value.
Japanese Unexamined Patent Publication No. 2003-121270 (paragraphs 0016 to 0023 and FIG. 3)

しかしながら、上記従来のアナログ入力切換回路８には、図５に示すように、外部電圧６に基づいたアナログ値（分圧されたアナログ電圧）と外部抵抗７に基づいたアナログ値（アナログ電圧）とを別々のＡ／Ｄポート８００，８０１に入力することから、同一のＡ／Ｄポート８００（又は８０１）に切換入力することができず、Ａ／Ｄポート８００，８０１を効率よく用いることができないという問題があった。また、従来のアナログ入力切換回路８には、外部接続端子８１〜８５の数が多くなってしまうという問題があった。このため、外部接続端子８１〜８５を形成するコネクタ（図示せず）の形状も大きくなり、これに伴って、実装面積も大きくなってしまう。   However, the conventional analog input switching circuit 8 includes an analog value based on the external voltage 6 (divided analog voltage) and an analog value based on the external resistor 7 (analog voltage), as shown in FIG. Are input to separate A / D ports 800 and 801, the same A / D port 800 (or 801) cannot be switched in and the A / D ports 800 and 801 cannot be used efficiently. There was a problem. Further, the conventional analog input switching circuit 8 has a problem that the number of external connection terminals 81 to 85 is increased. For this reason, the shape of the connector (not shown) that forms the external connection terminals 81 to 85 is also increased, and accordingly, the mounting area is also increased.

本発明は上記の点に鑑みて為されたものであり、その目的とするところは、マイコンのＡ／Ｄポートを効率よく用いることができるとともに外部接続端子の数を減らすことができるアナログ入力切換回路を提供することにある。   The present invention has been made in view of the above points, and an object of the present invention is to make analog input switching that can efficiently use an A / D port of a microcomputer and reduce the number of external connection terminals. It is to provide a circuit.

請求項１の発明は、アナログ値が入力されるＡ／Ｄポートを有するマイコンと、前記マイコンの電源電圧以下の電圧が印加される第１の外部接続端子と、前記Ａ／Ｄポートに接続される第２の外部接続端子と、一端が前記Ａ／Ｄポートに接続される第１の分圧抵抗と、前記第１の分圧抵抗の他端に接続される第３の外部接続端子と、グランドに接続される第４の外部接続端子と、第２の分圧抵抗及びスイッチが直列に接続され一端が前記第１の分圧抵抗の一端に接続され他端が前記グランドに接続される直列回路とを備えることを特徴とする。   The invention of claim 1 is connected to the A / D port, a microcomputer having an A / D port to which an analog value is input, a first external connection terminal to which a voltage equal to or lower than the power supply voltage of the microcomputer is applied. A second external connection terminal, a first voltage dividing resistor having one end connected to the A / D port, a third external connection terminal connected to the other end of the first voltage dividing resistor, A fourth external connection terminal connected to the ground, a second voltage dividing resistor and a switch are connected in series, one end is connected to one end of the first voltage dividing resistor, and the other end is connected to the ground. And a circuit.

請求項１の発明によれば、スイッチのオンオフの切り換えによって、外部電圧を測定する場合と外部抵抗の抵抗値を測定する場合に、外部接続端子から入力されるそれぞれのアナログ値を同一のＡ／Ｄポートに入力することができるので、外部電圧に基づいたアナログ値と外部抵抗に基づいたアナログ値とを別々のＡ／Ｄポートに入力する構成に比べて、マイコンのＡ／Ｄポートを効率よく用いることができる。また、外部電圧を測定する場合と外部抵抗の抵抗値を測定する場合とで、グランドに接続される外部接続端子を共用することができるので、従来のものより外部接続端子の数を減らすことができる。   According to the first aspect of the present invention, when the external voltage is measured and the resistance value of the external resistance is measured by switching the switch on and off, the analog values inputted from the external connection terminals are set to the same A / Since it can be input to the D port, the A / D port of the microcomputer is more efficient than the configuration in which the analog value based on the external voltage and the analog value based on the external resistance are input to separate A / D ports. Can be used. In addition, the external connection terminal connected to the ground can be shared for measuring the external voltage and the resistance value of the external resistance, so the number of external connection terminals can be reduced compared to the conventional one. it can.

まず、本発明の実施形態に係るアナログ入力切換回路の構成について図１を用いて説明する。このアナログ入力切換回路１は、図１（ａ）に示すように、外部電圧６又は外部抵抗７に基づいたアナログ電圧を用いて対象機器（図示せず）を制御するものであり、アナログ電圧が入力されるＡ／Ｄポート２０を有するマイコン２と、マイコン２の電源電圧Ｖｃｃと同等の電圧が印加される第１の外部接続端子３１と、Ａ／Ｄポート２０に接続される第２の外部接続端子３２と、一端がＡ／Ｄポート２０に接続される第１の分圧抵抗４と、第１の分圧抵抗４の他端に接続される第３の外部接続端子３３と、グランドに接続される第４の外部接続端子３４と、第２の分圧抵抗５０及びスイッチ５１が直列に接続され一端が第１の分圧抵抗４の一端に接続され他端がグランドに接続される直列回路５とを備えている。   First, the configuration of an analog input switching circuit according to an embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1A, the analog input switching circuit 1 controls a target device (not shown) using an analog voltage based on an external voltage 6 or an external resistor 7, and the analog voltage is The microcomputer 2 having the input A / D port 20, the first external connection terminal 31 to which a voltage equivalent to the power supply voltage Vcc of the microcomputer 2 is applied, and the second external connected to the A / D port 20 A connection terminal 32, a first voltage dividing resistor 4 having one end connected to the A / D port 20, a third external connection terminal 33 connected to the other end of the first voltage dividing resistor 4, and a ground The fourth external connection terminal 34 to be connected, the second voltage dividing resistor 50 and the switch 51 are connected in series, one end is connected to one end of the first voltage dividing resistor 4 and the other end is connected to the ground. Circuit 5.

マイコン２は、Ａ／Ｄポート２０の他に、Ａ／Ｄコンバータ（図示せず）などを備えている。Ａ／Ｄコンバータでは、電圧コンパレータ（図示せず）がＡ／Ｄポート２０から入力されたアナログ電圧を、直列抵抗ストリング（図示せず）によって作り出された基準電圧と比較してデジタル変換値を求めている。直列抵抗ストリングはＡ／Ｄコンバータ用の基準電圧端子とＡ／Ｄコンバータ用のグランド間に接続され、２端子間を１０２４段階の等価な電圧ステップにすることで基準電圧を作り出している。このようにして、マイコン２は、Ａ／Ｄポート２０から入力されたアナログ電圧をデジタル変換値に変換することができる。   The microcomputer 2 includes an A / D converter (not shown) in addition to the A / D port 20. In the A / D converter, a voltage comparator (not shown) compares an analog voltage input from the A / D port 20 with a reference voltage generated by a series resistor string (not shown) to obtain a digital conversion value. ing. The series resistor string is connected between the reference voltage terminal for the A / D converter and the ground for the A / D converter, and generates a reference voltage by making the two terminals have equivalent voltage steps of 1024 steps. In this way, the microcomputer 2 can convert the analog voltage input from the A / D port 20 into a digital conversion value.

第１の外部接続端子３１には、外部抵抗７の抵抗値を測定する場合に、この外部抵抗７の一端が接続される。一方、第２の外部接続端子３２には、外部抵抗７の抵抗値を測定する場合に、外部抵抗７の他端が接続される。このとき、第２の外部接続端子３２は、外部分圧抵抗７０を介して第４の外部接続端子３４に接続される。   When the resistance value of the external resistor 7 is measured, one end of the external resistor 7 is connected to the first external connection terminal 31. On the other hand, when measuring the resistance value of the external resistor 7, the other end of the external resistor 7 is connected to the second external connection terminal 32. At this time, the second external connection terminal 32 is connected to the fourth external connection terminal 34 via the external partial pressure resistor 70.

第３の外部接続端子３３には、外部電圧６を測定する場合に、この外部電圧６の陽極が接続される。一方、第４の外部接続端子３４には、外部電圧６の陰極が接続される。   When the external voltage 6 is measured, the third external connection terminal 33 is connected to the anode of the external voltage 6. On the other hand, the cathode of the external voltage 6 is connected to the fourth external connection terminal 34.

直列回路５のスイッチ５１は、ユーザの操作によって両端間の電気的接続のオンオフを切り換えるものである。外部電圧６を測定する場合にはスイッチ５１をオンにし、第１の分圧抵抗４と第２の分圧抵抗５０に外部電圧６を印加する。これに対して、外部抵抗７の抵抗値を測定する場合にはスイッチ５１をオフにする。   The switch 51 of the series circuit 5 switches on / off of the electrical connection between both ends by a user operation. When measuring the external voltage 6, the switch 51 is turned on, and the external voltage 6 is applied to the first voltage dividing resistor 4 and the second voltage dividing resistor 50. On the other hand, when measuring the resistance value of the external resistor 7, the switch 51 is turned off.

このような構成のアナログ入力切換回路１において、マイコン２の電源電圧Ｖｃｃは例えば３．３Ｖであり、Ａ／Ｄコンバータ用電源電圧も電源電圧Ｖｃｃと等しい。ここで、Ａ／Ｄコンバータ用電源電圧（＝電源電圧Ｖｃｃ）以上のアナログ電圧がＡ／Ｄポート２０に入力されるとデジタル変換値が不定となったり、Ａ／Ｄポート２０においてアナログ電圧の入力不良が発生したりする恐れがあることから、Ａ／Ｄポート２０に入力される最大アナログ電圧は電源電圧Ｖｃｃ以下でなければならない。   In the analog input switching circuit 1 having such a configuration, the power supply voltage Vcc of the microcomputer 2 is 3.3 V, for example, and the power supply voltage for the A / D converter is also equal to the power supply voltage Vcc. Here, when an analog voltage equal to or higher than the power supply voltage for the A / D converter (= power supply voltage Vcc) is input to the A / D port 20, the digital conversion value becomes unstable or the analog voltage is input to the A / D port 20. The maximum analog voltage input to the A / D port 20 must be equal to or lower than the power supply voltage Vcc because a failure may occur.

外部抵抗７の抵抗値を測定する場合、この外部抵抗７と外部分圧抵抗７０とで、第１の外部接続端子３１に印加されたマイコン２の電源電圧Ｖｃｃと同等の電圧が分圧され、この分圧された電圧がＡ／Ｄポート２０に入力されるので、Ａ／Ｄポート２０に入力されるアナログ電圧は、｛Ｒ４／（Ｒ３＋Ｒ４）｝×Ｖｃｃ（Ｒ３：外部抵抗７の抵抗値、Ｒ４：外部分圧抵抗７０の抵抗値、Ｖｃｃ：マイコン２の電源電圧）となり、Ａ／Ｄコンバータ用電源電圧つまり電源電圧Ｖｃｃを超えるという問題は生じない。なお、第１の外部接続端子３１に印加される電圧はマイコン２の電源電圧Ｖｃｃに限定されず、電源電圧Ｖｃｃ以下の大きさであってもよい。   When measuring the resistance value of the external resistor 7, a voltage equivalent to the power supply voltage Vcc of the microcomputer 2 applied to the first external connection terminal 31 is divided by the external resistor 7 and the external partial pressure resistor 70. Since this divided voltage is input to the A / D port 20, the analog voltage input to the A / D port 20 is {R4 / (R3 + R4)} × Vcc (R3: resistance value of the external resistor 7, R4: resistance value of the external partial pressure resistor 70, Vcc: power supply voltage of the microcomputer 2, and the problem of exceeding the power supply voltage for the A / D converter, that is, the power supply voltage Vcc does not occur. The voltage applied to the first external connection terminal 31 is not limited to the power supply voltage Vcc of the microcomputer 2 and may be a magnitude equal to or lower than the power supply voltage Vcc.

これに対して、外部電圧６を測定する場合、マイコン２の電源電圧Ｖｃｃ（例えば３．３Ｖ）を超える外部電圧６を直接Ａ／Ｄポート２０に入力することができない。このため、アナログ入力切換回路１において、第１の分圧抵抗４と第２の分圧抵抗５０とが外部電圧６を分圧し、この分圧した電圧をＡ／Ｄポート２０に入力させる必要がある。このときＡ／Ｄポート２０に入力されるアナログ電圧は、｛Ｒ２／（Ｒ１＋Ｒ２）｝×Ｖ（Ｒ１：第１の分圧抵抗４の抵抗値、Ｒ２：第２の分圧抵抗５０の抵抗値、Ｖ：外部電圧６）である。例えば、マイコン２の電源電圧Ｖｃｃが３．３Ｖである場合、外部電圧６が１０Ｖであったとき、第１の分圧抵抗４の抵抗値を６７０ｋΩ、第２の分圧抵抗５０の抵抗値を３３０ｋΩとすると、１０Ｖの外部電圧６ではなく３．３Ｖ（＝｛３３０ｋΩ／（６７０ｋΩ＋３３０ｋΩ）｝×１０Ｖ）に分圧された電圧をＡ／Ｄポート２０に入力させることができる。   On the other hand, when measuring the external voltage 6, the external voltage 6 exceeding the power supply voltage Vcc (for example, 3.3 V) of the microcomputer 2 cannot be directly input to the A / D port 20. For this reason, in the analog input switching circuit 1, the first voltage dividing resistor 4 and the second voltage dividing resistor 50 need to divide the external voltage 6, and this divided voltage needs to be input to the A / D port 20. is there. At this time, the analog voltage input to the A / D port 20 is {R2 / (R1 + R2)} × V (R1: resistance value of the first voltage dividing resistor 4, R2: resistance value of the second voltage dividing resistor 50) , V: external voltage 6). For example, when the power supply voltage Vcc of the microcomputer 2 is 3.3 V, when the external voltage 6 is 10 V, the resistance value of the first voltage dividing resistor 4 is 670 kΩ and the resistance value of the second voltage dividing resistor 50 is When 330 kΩ is set, a voltage divided to 3.3 V (= {330 kΩ / (670 kΩ + 330 kΩ)} × 10 V) instead of the external voltage 6 of 10 V can be input to the A / D port 20.

ところで、本実施形態のアナログ入力切換回路１には、外部入力インタフェースの第１〜４の外部接続端子３１〜３４を形成するものとして４ピンのコネクタ（図示せず）が用いられている。このコネクタはプリント基板（図示せず）に実装されて設けられる。本実施形態では、４ピンのコネクタを用いることができるので、従来（５ピンのコネクタ）よりもコネクタの形状を小さくすることができ、その結果、プリント基板上の実装面積の削減つまり省スペース化を図ることができる。   By the way, in the analog input switching circuit 1 of the present embodiment, a 4-pin connector (not shown) is used to form the first to fourth external connection terminals 31 to 34 of the external input interface. This connector is mounted on a printed board (not shown). In this embodiment, since a 4-pin connector can be used, the shape of the connector can be made smaller than that of the conventional (5-pin connector). As a result, the mounting area on the printed circuit board can be reduced, that is, the space can be saved. Can be achieved.

また、プリント基板（図示せず）には、コネクタ（図示せず）を実装できる箇所が複数設けられており、それぞれの箇所には、コネクタに代えてボリュームや端子台を実装できるように形成されている。上記より、コネクタに代えてボリュームや端子台を実装することも可能であり、実装段階でユーザの要望を取り入れて、容易にカスタマイズすることが可能である。   The printed circuit board (not shown) is provided with a plurality of locations where a connector (not shown) can be mounted, and each location is formed so that a volume or a terminal block can be mounted instead of the connector. ing. From the above, it is possible to mount a volume or a terminal block in place of the connector, and it is possible to easily customize it by incorporating the user's request at the mounting stage.

次に、本実施形態のアナログ入力切換回路１の動作について説明する。まず、外部電圧６を測定するときの動作について図１（ａ）を用いて説明する。外部電圧６は０Ｖ以上１０Ｖ以下とする。スイッチ５１がオンの状態で、第３の外部接続端子３３に外部電圧６の陽極が接続され、第４の外部接続端子３４に外部電圧６の陰極が接続される。このとき、第１の外部接続端子３１及び第２の外部接続端子３２は開放しておく。第１の分圧抵抗４及び第２の分圧抵抗５０で外部電圧６が分圧され、分圧された電圧がマイコン２のＡ／Ｄポート２０に入力される。マイコン２は、Ａ／Ｄポート２０から入力された電圧を用いて対象機器（図示せず）を制御する。   Next, the operation of the analog input switching circuit 1 of the present embodiment will be described. First, the operation when measuring the external voltage 6 will be described with reference to FIG. The external voltage 6 is 0V or more and 10V or less. With the switch 51 turned on, the anode of the external voltage 6 is connected to the third external connection terminal 33, and the cathode of the external voltage 6 is connected to the fourth external connection terminal 34. At this time, the first external connection terminal 31 and the second external connection terminal 32 are opened. The external voltage 6 is divided by the first voltage dividing resistor 4 and the second voltage dividing resistor 50, and the divided voltage is input to the A / D port 20 of the microcomputer 2. The microcomputer 2 controls a target device (not shown) using the voltage input from the A / D port 20.

続いて、外部抵抗７としてサーミスタ７１の抵抗値を測定するときの動作について図２を用いて説明する。図２のアナログ入力切換回路１は図１（ａ）と表現が異なっているが、図１（ａ）のアナログ入力切換回路１と同等のものである。スイッチ５１がオフの状態で、第１の外部接続端子３１にサーミスタ７１の一端が接続され、第２の外部接続端子３２にサーミスタ７１の他端及び外部分圧抵抗７０の一端が接続され、第４の外部接続端子３４に外部分圧抵抗７０の他端が接続される。このとき、第３の外部接続端子３３は開放しておく。サーミスタ７１及び外部分圧抵抗７０で、電源電圧Ｖｃｃと同様の電圧が分圧され、分圧された電圧が第２の外部接続端子３２を介してマイコン２のＡ／Ｄポート２０に入力される。マイコン２は、Ａ／Ｄポート２０から入力された電圧を用いて対象機器（図示せず）を制御する。   Next, the operation when measuring the resistance value of the thermistor 71 as the external resistor 7 will be described with reference to FIG. The analog input switching circuit 1 of FIG. 2 is equivalent to the analog input switching circuit 1 of FIG. 1A although the expression is different from that of FIG. With the switch 51 turned off, one end of the thermistor 71 is connected to the first external connection terminal 31, and the other end of the thermistor 71 and one end of the external partial pressure resistor 70 are connected to the second external connection terminal 32. The other end of the external partial resistance 70 is connected to the four external connection terminals 34. At this time, the third external connection terminal 33 is left open. A voltage similar to the power supply voltage Vcc is divided by the thermistor 71 and the external partial pressure resistor 70, and the divided voltage is input to the A / D port 20 of the microcomputer 2 via the second external connection terminal 32. . The microcomputer 2 controls a target device (not shown) using the voltage input from the A / D port 20.

また、図３のような場合も同様に、スイッチ５１がオフの状態で、マイコン２の電源電圧Ｖｃｃと同等の電圧がサーミスタ７１と外部分圧抵抗７０で分圧され、分圧された電圧がそのまま第２の外部接続端子３２からＡ／Ｄポート２０に入力される。   Similarly, in the case of FIG. 3, the voltage equivalent to the power supply voltage Vcc of the microcomputer 2 is divided by the thermistor 71 and the external partial pressure resistor 70 in the state where the switch 51 is off, and the divided voltage is obtained. The data is directly input from the second external connection terminal 32 to the A / D port 20.

続いて、外部抵抗７の抵抗値としてボリューム７２の抵抗値を測定するときの動作について図４を用いて説明する。図４のアナログ入力切換回路１は図１（ａ）と表現が異なっているが、図１（ａ）のアナログ入力切換回路１と同等のものである。スイッチ５１がオフの状態で、第１の外部接続端子３１にボリューム７２の固定端子の一方が接続され、第４の外部接続端子３４にボリューム７２の固定端子の他方が接続され、第２の外部接続端子３２にボリューム７２の可動端子が接続される。このとき、第３の外部接続端子３３は開放しておく。ボリューム７２の可動端子と固定端子の他端との間の電圧が第２の外部接続端子３２を介してマイコン２のＡ／Ｄポート２０に入力される。マイコン２は、この電圧を用いて対象機器（図示せず）を制御する。   Next, an operation when measuring the resistance value of the volume 72 as the resistance value of the external resistor 7 will be described with reference to FIG. The analog input switching circuit 1 in FIG. 4 is equivalent to the analog input switching circuit 1 in FIG. 1A although the expression is different from that in FIG. With the switch 51 turned off, one of the fixed terminals of the volume 72 is connected to the first external connection terminal 31, the other of the fixed terminals of the volume 72 is connected to the fourth external connection terminal 34, and the second external connection terminal 31 The movable terminal of the volume 72 is connected to the connection terminal 32. At this time, the third external connection terminal 33 is left open. A voltage between the movable terminal of the volume 72 and the other end of the fixed terminal is input to the A / D port 20 of the microcomputer 2 via the second external connection terminal 32. The microcomputer 2 controls a target device (not shown) using this voltage.

上記のようなアナログ入力切換回路１の各動作によって、図１（ｂ）に示すように、外部電圧６の測定と外部抵抗７の抵抗値の測定との間で、アナログ電圧の入力切換を容易に行うことができる。これにより、マイコン２の電源電圧Ｖｃｃ以上の外部電圧６に基づいたアナログ電圧と、外部抵抗７に基づいたアナログ電圧とを同一のＡ／Ｄポート２０で入力することができる。   By the operations of the analog input switching circuit 1 as described above, as shown in FIG. 1B, the analog voltage input can be easily switched between the measurement of the external voltage 6 and the resistance value of the external resistor 7. Can be done. Thereby, the analog voltage based on the external voltage 6 equal to or higher than the power supply voltage Vcc of the microcomputer 2 and the analog voltage based on the external resistor 7 can be input through the same A / D port 20.

以上、本実施形態によれば、スイッチ５１のオンオフの切り換えによって、マイコン２の電源電圧Ｖｃｃ以上の外部電圧６を測定する場合と外部抵抗７の抵抗値を測定する場合に、第２，３の外部接続端子３２，３３から入力されるアナログ電圧を同一のＡ／Ｄポート２０に入力することができるので、外部電圧６に基づいたアナログ電圧と外部抵抗７に基づいたアナログ電圧とを別々のＡ／Ｄポートに入力する構成に比べて、マイコン２のＡ／Ｄポート２０を効率よく用いることができる。また、外部電圧６を測定する場合と外部抵抗７の抵抗値を測定する場合とで、グランドに接続される外部接続端子を第４の外部接続端子３４で共用することができるので、従来のものより外部接続端子３１〜３４の数を減らすことができる。   As described above, according to the present embodiment, when the external voltage 6 equal to or higher than the power supply voltage Vcc of the microcomputer 2 is measured and the resistance value of the external resistor 7 is measured by switching the switch 51 on and off, Since the analog voltages input from the external connection terminals 32 and 33 can be input to the same A / D port 20, the analog voltage based on the external voltage 6 and the analog voltage based on the external resistor 7 are separated from each other by A. The A / D port 20 of the microcomputer 2 can be used more efficiently than the configuration for inputting to the / D port. Further, since the external connection terminal connected to the ground can be shared by the fourth external connection terminal 34 when measuring the external voltage 6 and when measuring the resistance value of the external resistor 7, the conventional one is used. In addition, the number of external connection terminals 31 to 34 can be reduced.

本発明の実施形態に係るアナログ入力切換回路において、（ａ）は外部電圧が接続された回路図、（ｂ）は状態の切り換えを示す図である。In the analog input switching circuit according to the embodiment of the present invention, (a) is a circuit diagram to which an external voltage is connected, and (b) is a diagram showing state switching. 同上に係るアナログ入力切換回路にサーミスタが接続された回路図である。It is the circuit diagram by which the thermistor was connected to the analog input switching circuit which concerns on the same as the above. 同上に係るアナログ入力切換回路にサーミスタが接続された他の回路図である。It is another circuit diagram by which the thermistor was connected to the analog input switching circuit which concerns on the same as the above. 同上に係るアナログ入力切換回路にボリュームが接続された回路図である。It is a circuit diagram in which a volume is connected to the analog input switching circuit according to the same. 従来のアナログ入力切換回路の回路図である。It is a circuit diagram of a conventional analog input switching circuit.

符号の説明Explanation of symbols

２ マイコン
２０ Ａ／Ｄポート
３１ 第１の外部接続端子
３２ 第２の外部接続端子
３３ 第３の外部接続端子
３４ 第４の外部接続端子
４ 第１の分圧抵抗
５ 直列回路
５０ 第２の分圧抵抗
５１ スイッチ
６ 外部電圧
７ 外部抵抗
７０ 外部分圧抵抗 2 Microcomputer 20 A / D port 31 1st external connection terminal 32 2nd external connection terminal 33 3rd external connection terminal 34 4th external connection terminal 4 1st voltage dividing resistor 5 Series circuit 50 2nd part Voltage resistance 51 Switch 6 External voltage 7 External resistance 70 External voltage dividing resistance

Claims (1)

アナログ値が入力されるＡ／Ｄポートを有するマイコンと、
前記マイコンの電源電圧以下の電圧が印加される第１の外部接続端子と、
前記Ａ／Ｄポートに接続される第２の外部接続端子と、
一端が前記Ａ／Ｄポートに接続される第１の分圧抵抗と、
前記第１の分圧抵抗の他端に接続される第３の外部接続端子と、
グランドに接続される第４の外部接続端子と、
第２の分圧抵抗及びスイッチが直列に接続され一端が前記第１の分圧抵抗の一端に接続され他端が前記グランドに接続される直列回路と
を備えることを特徴とするアナログ入力切換回路。 A microcomputer having an A / D port to which an analog value is input;
A first external connection terminal to which a voltage equal to or lower than the power supply voltage of the microcomputer is applied;
A second external connection terminal connected to the A / D port;
A first voltage dividing resistor having one end connected to the A / D port;
A third external connection terminal connected to the other end of the first voltage dividing resistor;
A fourth external connection terminal connected to the ground;
An analog input switching circuit comprising: a second voltage dividing resistor and a switch connected in series, one end connected to one end of the first voltage dividing resistor, and the other end connected to the ground. .
JP2007050091A 2007-02-28 2007-02-28 Analog input switching circuit Active JP4497166B2 (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS63113967U (en) * 1987-01-16 1988-07-22
JPH10289037A (en) * 1997-04-11 1998-10-27 Matsushita Electric Ind Co Ltd Battery voltage monitoring device and wireless printer
JP2001185233A (en) * 1999-12-27 2001-07-06 Fujitsu Kiden Ltd Detection circuit for battery voltage, battery pack and detection method of battery voltage
JP2003121270A (en) * 2001-10-12 2003-04-23 Rinnai Corp Temperature-detecting circuit communication device

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS63113967U (en) * 1987-01-16 1988-07-22
JPH10289037A (en) * 1997-04-11 1998-10-27 Matsushita Electric Ind Co Ltd Battery voltage monitoring device and wireless printer
JP2001185233A (en) * 1999-12-27 2001-07-06 Fujitsu Kiden Ltd Detection circuit for battery voltage, battery pack and detection method of battery voltage
JP2003121270A (en) * 2001-10-12 2003-04-23 Rinnai Corp Temperature-detecting circuit communication device

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