CD74HC646

The Harris CD74HC646 and CD74HC648 are octal bus transceivers/registers with three-state non-inverting outputs. The Harris CD74HC648 is an octal bus transceiver/register with three-state inverting outputs. CD74HC646 are bus transceivers with D-type flip-flops which act as internal storage registers. Data on the A bus or the B bus can be clocked into the registers on the LOW-to-HIGH transition of either CAB or CBA clock inputs. Outputs enable (OE) and direction (DIR) inputs control the transceiver functions. Data present at the high impedance output can be stored in either register or both but only one of the two buses can be enabled as outputs at any one time. The select controls (SAB and SBA) can multiplex stored and transparent (real time) data. The direction control determines which data bus will receive data when CD74HC646 output enable (OE) is LOW. In the high impedance mode (output enable HIGH), A data can be stored in one register and B data can be stored in the other register. The clocks are not gated with the direction (DIR) and output enable (OE) terminals; data at the A or B terminals can be clocked into the storage flip-flops at any time.