These devices are octal bus transceivers designed for asynchronous two-way data flow between the A and B busses. Both busses are capable of sinking 64 mA, have 3STATE outputs, and a common output enable pin. The direction of data flow is determined by the transmit/receive (T/R) input. The 74F645 is a high speed/low power version of the 74F245. The 74F640 is an inverting option of the 74F645.