SN74LS256J

The SN54/74LS256 is a Dual 4-Bit Addressable Latch with common control inputs; these include two Address inputs (A0, A1), an active LOW Enable input (E) and an active LOW Clear input (CL). Each latch has a Data input (D) and four outputs (Q0Q3).

When the Enable (E) is HIGH and the Clear input (CL) is LOW, all outputs (Q0Q3) are LOW. Dual 4-channel demultiplexing occurs when the (CL) and E are both LOW. When CL is HIGH and E is LOW, the selected output (Q0Q3), determined by the Address inputs, follows D. When the E goes HIGH, the contents of the latch are stored. When operating in the addressable latch mode (E=LOW, CL=HIGH), changing more than one bit of the Address (A0, A1) could impose a transient wrong address. Therefore, this should be done only while in the memory mode (E=CL=HIGH).