JPH0465577B

PURPOSE:To prevent to spend a wasteful transmission time by providing a negative acknowledge output means outputting 'zero' signals which continue for more than bit frame lengths as negative knowledges(NAK) in at least one station. CONSTITUTION:If a station A detects errors by a check code, a CPU4 outputs the negative knowledges(NAK) to an OR circuit 19. The negative knowledges(NAK) are the signals of '0' which continue for more than the bit frame lengths, but not the codes. Since they are the '0' signals, they are transmitted to a transmission line 2 prior to '1' signals. Since '0' by the negative acknowledge signals NAK are longer than the bit lengths, other transmission stations transmit mask signals and stops transmission when they at least transmit the 'once' of stop bits. Thus, a station B stops transmission by the negative acknowledges(NAK) of the station A. Consequently, the continuity of wasteful transmission is prevented and retransmission can immediately be executed.