M16CSLASH26 datasheet(169/239 Pages) RENESAS

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Renesas Technology Corp.

Programmable I/O Ports

163

M16C/26 Group

SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Under

development

Preliminary Specifications Rev. 0.9

Specifications in this manual are tentative and subject to change.

Programmable I/O Ports

There are 38 programmable I/O ports: P15 - P17, P6, P7, P8 (except P84), P90 - P93, and P10. 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.

Figures 1.17.1 to 1.17.3 show the programmable I/O ports. Figure 1.17.4 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, they function as outputs

regardless of the contents of the direction registers. See the descriptions of the respective functions for

how to set up the built-in peripheral devices.

(1) Direction registers

Figure 1.17.5 shows the port direction registers.

These registers are used to choose the direction of the programmable I/O ports. Each bit in these

registers corresponds one for one to each I/O pin.

Note: The Port 9 direction register incorporates a write protection function. Before writing to the port 9

direction register the write protection must be disabled by setting PRC2 of the Protect register (bit 2 at

000A16) to "1". Note that PRC2 is automatically reset to "0" after the next write to an SFR address.

(2) Port registers

Figure 1.17.6 shows the port registers.

These registers are used to read and write 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 the port registers corresponds one for one to each I/O pin.

(3) Pull-up control registers

Figure 1.17.7 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 to input.

(4) Port control register

Figure 1.17.8 shows the port control register.

Bit 0 of the port control register is used to control the read of port P1 as follows:

0 : When port P1 is set as an input port, the port input level is read.

When port P1 is set as an output port , the contents of the port P1 register are read.

1 : The contents of the port P1 register are always read.

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