Patent GB-1093518-A (GB)
Title: Error detection system
IPC: G11C29/52
Filed: 1966-04-15
Abstract: 1,093,518. Error detection in memory read-out devices. RADIO CORPORATION OF AMERICA. April 15, 1966 [April 29, 1965], No. 16619/66. Headings G4A and G4C. A memory system having error checking means comprises a memory ROM having an address register AR and a data register DR, the words stored in the memory including data words, a test word and an inverted test word, each word containing an indication of the classification of the following word, test decoder means 26 coupled to the data register to determine the classification of the next following word, storage means 36, 38 coupled to outputs of the test decoder means and having outputs for information word, a test word and inverted test word, memory word decoder means 52 coupled to all portions of the data register and having outputs for an information word, a test word and an inverted test word, and error indicating means coupled to the storage means and word decoder means to generate an error signal when the output of the word decoder means does not agree with the output of the storage means. In one embodiment (Fig. 1) an address in register AR causes a word to be taken from the memory, which may be a read-only memory, and stored in register DR at time t o . The word includes portions NA giving the address of the next word and F<SP>1</SP> indicating the classification of the next word. Parts F, F<SP>1</SP> pass to a function decoder to determine machine operation, part NA passes to an address decoder, then to an address generator and, via AND gate 22 at time t 2 , to the address register. The part F<SP>1</SP> is coupled to the test decoder 26. If the following word is a test word flip-flop 38 is set at time t 3 , if the following word is an inverted test word flip-flop 36 is set, otherwise both flip-flops are reset. The full word in register DR is also applied to decoder 52. Preferably the test word is all ones and the inverted test word is all zeros although other words can be used as long as one is complementary to the other. If the word detected is the test word e.g. all ones decoder gives an output on the " 1 " line, if the inverted test word is detected decoder 52 gives an output on the " O " line, otherwise outputs appear on lines #0, #1. If the first word detected is a data word and is to be followed by a test word, decoder 52 has outputs on lines #0, #1, flipflops 36, 38 will be reset and none of the AND gates #00, #00, #11, #11 connected to the two decoders 26, 52 will be enabled. At time t 2  the next address enters the register AR gate 22 being enabled by the inverters connected to OR gate 39, at time t 3  the decoder causes flip-flop 38 to be set since a test word is the next word. At the next time t o  the new word is read out of memory and applied to decoder 52 to cause an output on line 1. Again none of the AND gates are enabled. At time t 2  AND gate 22 is enabled, since the test word would always carry a next address of all ones, and gate 44 is enabled causing the previous address to be incremented by one. If a fault occurs in one of the gates, decoders or flip-flops one of the decoders would produce a different output to the other and would create an alarm signal. A second embodiment (Fig. 2, not shown) uses the next address decoder to perform the operations of the test decoder of Fig. 1. The address decoder also recognizes the test word and then uses this data to generate the next address.