99
3.11 Watchdog Function
3.11 Watchdog Function
The watchdog function detects program crashes.
If A5
H
and 5A
H
are not written to the watchdog reset postpone register within the
specified time due to a program crash, the watchdog timer issues a watchdog reset
request.
■
Watchdog Controller Block Diagram
Figure 3.11.1 is a watchdog controller block diagram.
Figure 3.11-1 Watchdog Timer Block Diagram
■
Starting the Watchdog Timer
Writing to the watchdog control register (WTCR) causes the watchdog timer to start operation.
For this operation, set the interval time of the watchdog timer using the WT1 and WT0 bits. The
interval time set first is valid but subsequent settings are ignored.
[Example]
■
Postponing Resetting
Once the watchdog timer starts operation, a program must regularly write A5H and 5AH to the
watchdog reset postpone register (WPR). The watchdog reset flip-flop stores the falling edge of
the tap selected by the timebase timer. If the flip-flop has not been cleared at the second falling
edge, a reset signal is generated.
Figure 3.11.2 shows the watchdog timer operation timing.
WPR
RSRR
A5&5A
WDOG
clr
CTBR
WTx
and
Internal bus
Timebase timer
frequency division
output
Latch
Select
Edge
sense
circuit
Watch
dog
F/F
State tr
ansition control circuit
Timebase timer
Reset state transition
request signal
State decoder
Reset state
Reset
causing
F/F
Timebase timer
frequency division
output
Internal reset
LDI:8
#00000010b,R1
; WT1,0=10
LDI:20
#WTCR,R2
STB
R1,@R2
; Starts the watchdog timer.
Summary of Contents for MB91F109
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Page 3: ...FUJITSU LIMITED FR30 32 Bit Microcontroller MB91F109 Hardware Manual ...
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Page 10: ...vi ...
Page 24: ...xx ...
Page 96: ...72 CHAPTER 2 CPU ...
Page 224: ...200 CHAPTER 4 BUS INTERFACE ...
Page 234: ...210 CHAPTER 5 I O PORTS ...
Page 268: ...244 CHAPTER 9 U TIMER ...
Page 290: ...266 CHAPTER 10 UART ...
Page 314: ...290 CHAPTER 12 16 BIT RELOAD TIMER ...
Page 322: ...298 CHAPTER 13 BIT SEARCH MODULE ...
Page 392: ...368 CHAPTER 16 FLASH MEMORY ...
Page 432: ...408 APPENDIX E Instructions F Table E 2 Instruction Formats OP rel11 5 11 ...
Page 448: ...424 APPENDIX E Instructions ...
Page 449: ...425 INDEX INDEX The index follows on the next page This is listed in alphabetic order ...
Page 458: ...434 INDEX ...
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Page 461: ...FUJITSU SEMICONDUCTOR FR30 32 Bit Microcontroller MB91F109 Hardware Manual ...