Z80 Datasheet, PDF (200/330 Pages) Zilog, Inc. – Z80 CPU PERIPHERALS

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PIN DESCRIPTION
Figure 3 illustrates a diagram of the Z80 PIO pin configuration. This
section describes the function of each pin.
D7-D0
Z80 CPU Data Bus (bidirectional, tristate). This bus is used to transfer all
data and commands between the Z80 CPU and the Z80 PIO. D0 is the
least-significant bit of the bus.
B/A Sel
Port B or A Select (input, active High). This pin defines which port is
accessed during a data transfer between the Z80 CPU and the Z80 PIO. A
Low level on this pin selects Port A while a High level selects Port B.
Often, Address bit A0 from the CPU is used for this selection function.
C/D Sel
Control or Data Select (input, active High). This pin defines the type of
data transfer to be performed between the CPU and the PIO. A High level
on this pin during a CPU write to the PIO causes the Z80 data bus to be
interpreted as a command for the port selected by the B/A Select line. A
Low level on this pin means that the Z80 data bus is being used to transfer
data between the CPU and the PIO. Often, Address bit Al from the CPU is
used for this function.
CE
Chip Enable (input, active Low). A Low level on this pin enables the PIO to
accept command or data inputs from the CPU during a write cycle or to
transmit data to the CPU during a read cycle. This signal is generally a decode
of four I/O port numbers that encompass Ports A and B, data, and control.
UM008101-0601
Parallel Input/Output