A memory write operation starts with the CPU asserting MA=1 and RD=0, putting the address where to write the byte on the address wires, and the actual byte to write on the data wires. The memory responds internally when it "sees" MA is 1 and it absorbs all these values and stores the value. In some cases, the CPU may simply start the memory on a write and then go off to do other useful work. For a read, however, the CPU must wait the full amount of time for the memory to fetch the desired value.