| 摘要 |
1,176,253. Telegraphy. SIEMENS A.G. 27 Sept., 1967 [28 Sept., 1966], No. 43887/67. Heading H4P. In a telegraph system in which transmitted characters can be checked for error, e.g. by parity, the receiver checks each character for error and if no error is found each bit is checked to detect error not revealed by the character check. In the embodiment described, transitions in the received character, which includes a parity bit, are passed to first and second bi-stables which are enabled for a time lying symmetrically about each theoretical mid-bit point. The first bi-stable changes state if a transition occurs while it is enabled, and it remains in this state. The second bi-stable changes state at each transition when enabled, thus making an odd/even count of these transitions. If, at the end of the character, there is an even count, i.e. it is possible that the character is faulty although the character parity check has revealed no error, and if the first bi-stable has changed state an error-indicating signal is generated. Reference is made to the use of constant ratio code, and codes with various Hamming distances. The bit checking arrangement may include a threshold unit. |
