The 'ABT16657 contain two noninverting octal transceiver sections with separate parity generator/checker circuits and control signals. For either section, the transmit/receive (1T/R\ or 2T/R\) input determines the direction of data flow. When 1T/R\ (or 2T/R\) is high, data flows from the 1A (or 2A) port to the 1B (or 2B) port (transmit mode); when 1T/R\ (or 2T/R\) is low, data flows from the 1B (or 2B) port to the 1A (or 2A) port (receive mode). When the output-enable (1or 2) input is high, both the 1A (or 2A) and 1B (or 2B) ports are in the high-impedance state.

Odd or even parity is selected by a logic high or low level, respectively, on the 1ODD(or 2ODD) input. 1PARITY (or 2PARITY) carries the parity bit value; it is an output from the parity generator/checker in the transmit mode and an input to the parity generator/checker in the receive mode.

In the transmit mode, after the 1A (or 2A) bus is polled to determine the number of high bits, 1PARITY (or 2PARITY) is set to the logic level that maintains the parity sense selected by the level at the 1ODD(or 2ODD) input. For example, if 1ODDis low (even parity selected) and there are five high bits on the 1A bus, then 1PARITY is set to the logic high level so that an even number of the nine total bits (eight 1A-bus bits plus parity bit) are high.Read more