4524_M Datasheet, PDF (212/310 Pages) Renesas Technology Corp – 4-BIT CISC SINGLE-CHIP MICROCOMPUTER 720 FAMILY / 4500 SERIES

4524 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]
↓
( ) 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
In the interrupt service routine, do not clear watchdog timer flag WDF1.
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
; POF instruction enabled
POF
↓
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 goes into RAM back-up mode, microcomputer may
be reset.
When watchdog timer and RAM back-up mode are used, execute the WRST instruction to initialize WDF1 flag before
system goes into the RAM back-up mode.
Fig. 2.3.10 Watchdog timer setting example
Rev.2.00 Aug, 06 2004
REJ09B0107-0200Z
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