Mitsubishi microcomputers
M16C / 62A Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Programmable I/O Port
161
Programmable I/O Ports
There are 87 programmable I/O ports: P0 to P10 (excluding P8
5
). Each port can be set independently for
input or output using the direction register. A pull-up resistance for each block of 4 ports can be set. P8
5
is
an input-only port and has no built-in pull-up resistance.
Figures 1.20.1 to 1.20.4 show the programmable I/O ports. Figure 1.20.5 shows the I/O pins.
Each pin functions as a programmable I/O port and as the I/O for the built-in peripheral devices.
To use the pins as the inputs for the built-in peripheral devices, set the direction register of each pin to input
mode. When the pins are used as the outputs for the built-in peripheral devices (other than the D-A con-
verter), they function as outputs regardless of the contents of the direction registers. When pins are to be
used as the outputs for the D-A converter, do not set the direction registers to output mode. See the
descriptions of the respective functions for how to set up the built-in peripheral devices.
(1) Direction registers
Figure 1.20.6 shows the direction registers.
These registers are used to choose the direction of the programmable I/O ports. Each bit in these regis-
ters corresponds one for one to each I/O pin.
Note: There is no direction register bit for P8
5
.
(2) Port registers
Figure 1.20.7 shows the port registers.
These registers are used to write and read data for input and output to and from an external device. A
port register consists of a port latch to hold output data and a circuit to read the status of a pin. Each bit
in port registers corresponds one for one to each I/O pin.
(3) Pull-up control registers
Figure 1.20.8 shows the pull-up control registers.
The pull-up control register can be set to apply a pull-up resistance to each block of 4 ports. When ports
are set to have a pull-up resistance, the pull-up resistance is connected only when the direction register is
set for input.
However, in memory expansion mode and microprocessor mode, the pull-up control register of P0 to P3,
P4
0
to P4
3
, and P5 is invalid.
(4) Port control register
Figure 1.20.9 shows the port control register.
The bit 0 of port control resister is used to read port P1 as follows:
0 : When port P1 is input port, port input level is read.
When port P1 is output port , the contents of port P1 register is read.
1 : The contents of port P1 register is read always.
This register is valid in the following:
External bus width is 8 bits in microprocessor mode or memory expansion mode.
Port P1 can be used as a port in multiplexed bus for the entire space.