Mitsubishi microcomputers
M16C / 6N0 / 6N1 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
196
Programmable I/O Port
There are 87 programmable I/O ports: P0 to P10 (excluding P85). 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. P71 and
P91 are Nch open drain ports and have no built-in pull-up resistance. P85 is an input-only port and has no
built-in pull-up resistance.
Figures 1.21.1 to 1.21.4 show the programmable I/O ports. Figure 1.21.5 shows the input 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 the 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 1.21.6 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)
In memory expansion and microprocessor mode, the contents of corresponding direction register of pins
_______
_____
________ ______
________ _______
________ __________ __________
A0 to A19, D0 to D15, CS0 to CS3, RD, WRL/WR, WRH/BHE, ALE, RDY, HOLD, HLDA and BCLK cannot
be modified.
Note: There is no direction register bit for P85.
(2) Port registers
Figure 1.21.7 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.
In memory expansion and microprocessor mode, the contents of corresponding direction register of pins
_______
_____
________ ______
________ _______
________ __________ __________
A0 to A19, D0 to D15, CS0 to CS3, RD, WRL/WR, WRH/BHE, ALE, RDY, HOLD, HLDA and BCLK cannot
be modified.
(3) Pull-up control registers
Figure 1.21.8 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,
P40 to P43, and P5 is invalid.
The contents of register can be changed, but the pull-up resistance is not connected.
Programmable I/O Port