| 摘要 |
PURPOSE:To reduce the number of ICs for a read-only memory (ROM) by storing data with detection information added to its end without providing a parity bit to each byte. CONSTITUTION:At the end of ROMI, a horizontal parity byte, for example, obtained by adding respective bits bit by bit is written as error detection information byte 7. At every time when data are transmitted from buffer register 2 to arithmetic unit 4, the bit addition to the contents of accumulator 5 is done and, on the other hand, counter 6 counts up its contents by +1. Therefore, if the data has no error, the contents of accumulator 5 becomes a newly-calculated error detection information byte when the value of counter 6 becomes extremely close to the error detection information byte. For the purpose, when byte 7 is read out from ROM1, the comparison with the contents of accumulator 5 which have been calculated yet is done and if they disagree, the data is regarded as an error. |
