GB1255432A - An adapter - Google Patents

Abstract

1,255,432. Telegraphy. INTERNATIONAL BUSINESS MACHINES CORP. 17 March, 1970 [2 April, 1969], No. 12649/70. Heading H4P. A telegraph receiver which can receive startstop-signals at various bit-rates tests for the presence of the stop bit in a received character at the time expected according to the bit-rate at which the receiver is set and if absent the receiver is reset to either an alternative bit-rate or in another arrangement to one of a number of bit-rates which the receiver successively tries. The receiver is under the control of a processor which initially puts the receiver into a receive state. The next received character start bit, identified by a mark/space transition, set to a count of 5 a 3-stage binary counter driven by clock pulses. Upon the count of 7, and subsequent counts of 7, the state of the received signal is sampled and signalled to the processor. After receiving the number of samples equal to the character bit-length corresponding to the character speed to which the receiver is set the processor instructs the receiver to sample what should then be a stop, indicated by a mark. Failure to detect a mark causes the receiver to be reset for the next character with the counter driven at a different clock rate corresponding to a slower bit rate. In one arrangement only two clock frequencies are available but in another arrangement a shift register is clocked on one stage to gate one of several frequencies to the counter. In a further arrangement a counter acting through a decoder selects the frequencies as the same character is successively tested for its stop at different possible stop times. In all arrangements a condition of the character coding is that no character may not have a bit at the mark level when it is time for the stop bit (mark) of a higher rate character.