38K2 datasheet(155/358 Pages) RENESAS

155 / 358 page

2.1 I/O port

Rev.2.00

Oct 15, 2006

page 6 of 112

38K2 Group

REJ09B0338-0200

APPLICATION

2.1.4 Notes on input and output pins

(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 a bit which is set for an input port :

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

• As for a bit which is set for an output port :

The bit value of the port latch 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 the port latch 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) 155 Page - Renesas Technology Corp