The MM54C89 MM74C89 is a 16-word by 4-bit random access read write memory Inputs to the memory consist of four address lines four data input lines a write enable line and a memory enable line The four binary address inputs are decoded internally to select each of the 16 possible word locations An internal address register latches the address information on the positive to negative transition of the memory enable input The four TRI-STATE data output lines working in conjunction with the memory enable input provide for easy memory expansion Address Operation Address inputs must be stable tSA prior to the positive to negative transition of memory enable It is thus not necessary to hold address information stable for more than tHA after the memory is enabled (positive to negative transition of memory enable) Note The timing is different than the DM7489 in that a positive to negative transition of the memory enable must occur for the memory to be selected