4507_M Datasheet, PDF (147/216 Pages) Renesas Technology Corp – 4-BIT CISC SINGLE-CHIP MICROCOMPUTER 4500 SERIES

4507 Group
APPLICATION
2.3 Timers
Main routine (every 20 ms)
➀ Reset Flag WDF1
Watchdog timer flag WDF1 is reset.
“0”
Watchdog timer flag WDF1 cleared
(WRST instruction)
Note when the watchdog timer flag is cleared
When ➀ is executed, considering the skip of the next instruction according to the
watchdog timer flag WDF1, insert the NOP instruction after the WRST instruction.
Main routine execution
Repeat
Do not clear watchdog timer WDF1 flag in interrupt service routine.
Interrupt may be executed even if program run-away occurs.
When going to RAM back-up mode
••••••
WRST
; WDF flag cleared
NOP
DI
; Interrupt disabled
EPOF
; POF2 instruction enabled
POF2
↓
Oscillation stop (RAM back-up mode)
In the RAM back-up mode, WEF, WDF1 and WDF2 flags are initialized. However, when WDF2 flag is set to “1”, at the
same time, system enters RAM back-up mode, microcomputer may be reset. When watchdog timer and RAM back-up
mode are used, execute the WRST instruction before system enters the RAM back-up mode to initialize WDF1 flag.
Fig. 2.3.8 Watchdog timer setting example
2.3.4 Notes on use
(1) Prescaler
Stop the prescaler operation to change its frequency dividing ratio.
(2) Count source
Stop timer 1 or 2 counting to change its count source.
(3) Reading the count values
Stop timer 1 or 2 counting and then execute the TAB1 or TAB2 instruction to read its data.
Rev.2.01 Feb 04, 2005
REJ09B0195-0201
2-32