The first button: 1=write, 0=read
The next four are the 4-bit data input.
On write statement the memory cells get the data from inputs. On read, they charge the data to the 4bit-4DFlipFlops Latch. This can be useful to create a second circuit to refresh the data, passing the bits to the capacitor as whe do on writing state (in a time of 1s/s the data is lost in less than 5 seconds).
