These TRI-STATE bi-directional buffers utilize advanced silicon-gate CMOS technology and are intended for two-way asynchronous communication between data buses They have high drive current outputs which enable high speed operation even when driving large bus capacitances These circuits possess the low power consumption and high noise immunity usually associated with CMOS circuitry yet have speeds comparable to low power Schottky TTL circuits Each device has an active low enable G and a direction control input DIR When DIR is high data flows from the A inputs to the B outputs When DIR is low data flows from the B inputs to the A outputs The MM54HC640 MM74HC640 transfers inverted data from one bus to other and the MM54HC643 MM74HC643 transfers inverted data from the A bus to the B bus and true data from the B bus to the A bus