GB1186416A - Improvements in or relating to Electrical Intelligence Storage Equipment - Google Patents

Abstract

1,186,416. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. 24 Aug., 1967, No. 39051/67. Heading H4K. [Also in Division G4] In a data store having asscoiated read, write and processing circuitry, the latter is subjected to routine testing by: reading-out a word from a selected location in the store, storing the word in a temporary memory, processing the word, e.g. by inverting 0 and 1 bits and rewriting the modified word into the store at the originally selected location; reading-out the modified word and subjecting it to further processing whereby the word as originally read-out should be obtained, and writing this word back into the store; and finally reading-out the word once more, comparing it with the word stored in the temporary memory and then rewriting it again if all is well. The three stages of the test are performed during three successive access cycles of the store's address register. The test is applied whilst the store is in normal use but preferably just before a particular word location is required to be used. Alternatively the words can be tested successively during each word's "dead time ". More than one temporary memory together with additional logic can be used for processing the data words. Audible or visual alarms are given if a fault is found at any stage of the test. The invention is applicable to stores used in a general purpose computer (Fig. 1, not shown), to metering pulse stores in a telephone exchange where the processing circuitry consists in ADD 1 and SUBTRACT 1 logic (Fig. 2, not shown), or to the speech stores required at the intersections of highways in a PCM telephone system (Fig. 3, not shown). In the latter case testing takes three frames and the word location under test is busied against use by subscribers even if a conversation involving the use of this word location is in progress. Normally testing is not allowed to commence until the word location has been unused for a preset period and if the said period does not occur within a determined time testing of this location is abandoned and testing of the next location is commenced. The store may comprise a matrix of ferrite cores or be a thin film magnetic memory.