This block has the logic to buffer the data bus to/from the microprocessor, and to the internal registers. It contains 8 input pins, usually labelled such as D7........D0, where D7 is the MSB.
The Read/Write Logic block contains 5 pins, which are given below. Notice that X\denotes an active low signal.
o RD\: read signal
o WR\: write signal
o CS\: chip select signal
o A0, A1: address lines
Operation mode of the PIT is altered by setting the above hardware signals. For instance, to write to the Control Word Register, one have to set CS\ = 0, RD\ = 1, WR\ = 0, A1 = A0 = 1.