MM74C89

MM74C89 64-Bit 3-STATE Random Access Read/Write Memory October 1987 Revised January 1999 MM74C89 64-Bit 3-STATE Random Access Read/Write Memory General Description The 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 3-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). Write Operation: Information present at the data inputs is written into the memory at the selected address by bringing write enable and memory enable LOW. Read Operation: The complement of the information which was written into the memory is non-destructively read out at the four outputs. This is accomplished by selecting the desired address and bringing memory enable LOW and write enable HIGH. When the device is writing or disabled the output assumes a 3-STATE (Hi-z) condition. Features s Wide supply voltage r...