参数资料
型号: M34509G4HFP
元件分类: 微控制器/微处理器
英文描述: 4-BIT, OTPROM, 6 MHz, MICROCONTROLLER, PDSO24
封装: 5.30 X 10.10 MM, 0.80 MM PITCH, PLASTIC, SSOP-24
文件页数: 112/143页
文件大小: 1056K
代理商: M34509G4HFP
Rev.1.03
2009.07.27
page 70 of 140
REJ03B0147-0103
4509 Group
Fig. 72 Watchdog timer by software
<The main routine>
Assigns a single word of RAM to a software watchdog timer
(SWDT) and writes the initial value N in the SWDT once at each
execution of the main routine. The initial value N should satisfy the
following condition:
N+1 ≥ (Counts of interrupt processing executed in each main rou-
tine)
As the main routine execution cycle may change because of an in-
terrupt processing or others, the initial value N should have a
margin.
Watches the operation of the interrupt processing routine by com-
paring the SWDT contents with counts of interrupt processing after
the initial value N has been set.
Detects that the interrupt processing routine has failed and deter-
mines to branch to the program initialization routine for recovery
processing in the following case:
If the SWDT contents do not change after interrupt processing.
<The interrupt processing routine>
Decrements the SWDT contents by 1 at each interrupt processing.
Determines that the main routine operates normally when the
SWDT contents are reset to the initial value N at almost fixed
cycles (at the fixed interrupt processing count).
Detects that the main routine has failed and determines to branch
to the program initialization routine for recovery processing in the
following case:
If the SWDT contents are not initialized to the initial value N but
continued to decrement and if they reach 0 or less.
Main routine
(SWDT)← N
EI
Main processing
(SWDT)
Interrupt processing
routine errors
N
Interrupt processing routine
(SWDT) ← (SWDT)—1
Interrupt processing
(SWDT)
Main routine
errors
>0
≤0
RTI
Return
=N?
≤0?
≠N
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