M16C80 Datasheet, PDF (234/358 Pages) Renesas Technology Corp – RENESAS 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/80 SERIES

M16C/80 Group
27. Usage Precaution
Microprocesser mode or Memory expansion mode
When the MCU enters wait mode while operating in memory expansion mode or microprocessor
mode, a pin functioning as part of the address or data bus retains it's state on the bus before wait mode
is entered. Shift to single-chip mode and output an arbitrary value in order to reduce current consumption.
By shifting to single-chip mode, a pin which was functioning as part of the bus becomes a general-
purpose port and can output an arbitrary value. Set the port registers and direction registers after shifting
_____ _____ _____
to single-chip mode (this implies that any control pins (CS,WR,RD,etc.. ) being used for access of an
external device be changed as well).
If the port registers and direction registers are set while in memory expansion mode or microprocessor
mode, the operation will be ignored.
This is similar when entering stop mode.
Setting procedure is following.
Operate in memory expansion mode or microprocessor mode
Shift to single-chip mode
Set the port register
Set the direction register
Enter the wait mode or stop mode
Note
Note . This program does not work in external area. Transfer a program to
internal RAM and work on internal RAM.
Figure 27.3 Setting procedure of the port register and direction register.
Microprocessor
If the software reset is executed when the CNVss pin is connected to Vcc to start up in microprocessor
mode, write at least three NOP instructions following the writing instruction to the PM0 Register.
example:
mov.b #02H,PRCR
bset 3,PM0 ; or "mov.b #8BH,PM0" (instruction to execute software reset)
nop
; write at least three NOP instructions
nop
nop
nop
Rev.1.00 Aug. 02, 2005 ^{Page 223} of 329
REJ09B0187-0100