MC54F256

The MC54/74F256 dual addressable latch has four distinct modes of operation which are selectable by controlling the Clear and Enable inputs (see Function Table). In the addressable latch mode, data at the Data (D) inputs is written into the addressed latches. The addressed latches of MC54/74F256 will follow the  Data input with all unaddressed latches remaining in their previous states.

In the memory mode, all latches of MC54/74F256 remain in their previous states and are unaffected by the Data or Address inputs. To eliminate the possibility of entering erroneous data in the latches, the enable should be held HIGH (inactive) while the address lines are changing. In the dual 1-of-4 decoding or demultiplexing mode (MR = E = LOW), addressed outputs will follow the level of the D inputs with all other outputs LOW. In the clear mode, all outputs of MC54/74F256 are LOW and uneffected by the Address and Data inputs.