參數(shù)資料
型號： MB90F949APF
元件分類： 微控制器/微處理器
英文描述： MICROCONTROLLER, PQFP100
封裝： 14 X 20 MM, 3.35 MM HEIGHT, 0.65 MM PITCH, PLASTIC, QFP-100
文件頁數(shù)： 24/57頁
文件大?。?/td> 1586K
代理商： MB90F949APF
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
7544 Group
MITSUBISHI MICROCOMPUTERS
30
PRELIMINAR
Y
Notice:
This
is not
a final
specification.
Some
parametric
limits
are
subject
to change.
Watchdog Timer
The watchdog timer gives a means for returning to a reset status
when the program fails to run on its normal loop due to a runaway.
The watchdog timer consists of an 8-bit watchdog timer H and an
8-bit watchdog timer L, being a 16-bit counter.
Standard operation of watchdog timer
The watchdog timer stops when the watchdog timer control regis-
ter (address 003916) is not set after reset. Writing an optional
value to the watchdog timer control register (address 003916)
causes the watchdog timer to start to count down. When the
watchdog timer H underflows, an internal reset occurs. Accord-
ingly, it is programmed that the watchdog timer control register
(address 003916) can be set before an underflow occurs.
When the watchdog timer control register (address 003916) is
read, the values of the high-order 6-bit of the watchdog timer H,
STP instruction disable bit and watchdog timer H count source se-
lection bit are read.
Initial value of watchdog timer
By a reset or writing to the watchdog timer control register (ad-
dress 003916), the watchdog timer H is set to “FF16” and the
watchdog timer L is set to “FF16”.
Operation of watchdog timer H count source selection bit
A watchdog timer H count source can be selected by bit 7 of the
watchdog timer control register (address 003916). When this bit is
“0”, the count source becomes a watchdog timer L underflow sig-
nal. The detection time is 131.072 ms at f(XIN)=8 MHz.
When this bit is “1”, the count source becomes f(XIN)/16. In this
case, the detection time is 512
s at f(XIN)=8 MHz.
This bit is cleared to “0” after reset.
Operation of STP instruction disable bit
When the watchdog timer is in operation, the STP instruction can
be disabled by bit 6 of the watchdog timer control register (ad-
dress 003916).
When this bit is “0”, the STP instruction is enabled.
When this bit is “1”, the STP instruction is disabled, and an inter-
nal reset occurs if the STP instruction is executed.
Once this bit is set to “1”, it cannot be changed to “0” by program.
This bit is cleared to “0” after reset.
Fig. 33 Block diagram of watchdog timer
Fig. 34 Structure of watchdog timer control register
XIN
Data bus
“0”
“1”
1/16
Watchdog timer H count
source selection bit
Reset
circuit
STP Instruction disable bit
Watchdog timer H (8)
Write "FF16" to the
watchdog timer
control register
Internal reset
RESET
Watchdog timer L (8)
STP Instruction
Write “FF16” to the
watchdog timer
control register
Watchdog timer control register
(WDTCON: address 003916, initial value: 3F16)
Watchdog timer H (read only for high-order 6-bit)
STP instruction disable bit
0 : STP instruction enabled
1 : STP instruction disabled
Watchdog timer H count source selection bit
0 : Watchdog timer L underflow
1 : f(XIN)/16
b7
b0
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