38K2 datasheet(281/358 Pages) RENESAS

281 / 358 page

3.2 Notes on use

Rev.2.00

Oct 15, 2006

page 20 of 99

38K2 Group

REJ09B0338-0200

APPENDIX

3.2 Notes on use

3.2.1 Notes on input and output ports

(1)

Modifying output data with bit managing instruction

When the port latch of an I/O port is modified with the bit managing instruction✽1, the value of the

unspecified bit may be changed.

q Reason

The bit managing instructions are read-modify-write form instructions for reading and writing data

by a byte unit. Accordingly, when these instructions are executed on a bit of the port latch of an

I/O port, the following is executed to all bits of the port latch.

•As for bit which is set for input port:

The pin state is read in the CPU, and is written to this bit after bit managing.

•As for bit which is set for output port:

The bit value is read in the CPU, and is written to this bit after bit managing.

Note the following:

•Even when a port which is set as an output port is changed for an input port, its port latch holds

the output data.

•As for a bit of which is set for an input port, its value may be changed even when not specified

with a bit managing instruction in case where the pin state differs from its port latch contents.

✽1 Bit managing instructions: SEB and CLB instructions

38K2 Datasheet(PDF) 281 Page - Renesas Technology Corp