參數(shù)資料
型號： M37531
廠商： Mitsubishi Electric Corporation
英文描述： Single Chip 8 Bits CMOS Microcomputer(8位單片機)
中文描述： 單芯片的CMOS 8位單片機（8位單片機）
文件頁數(shù)： 27/64頁
文件大?。?/td> 631K
代理商： M37531
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
7531 Group
MITSUBISHI MICROCOMPUTERS
27
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 register
(address 0039
16
) is not set after reset. Writing an optional value to
the watchdog timer control register (address 0039
16
) causes the
watchdog timer to start to count down. When the watchdog timer H
underflows, an internal reset occurs. Accordingly, it is programmed
that the watchdog timer control register (address 0039
16
) can be set
before an underflow occurs.
When the watchdog timer control register (address 0039
16
) is read,
the values of the high-order 6-bit of the watchdog timer H, STP in-
struction disable bit and watchdog timer H count source selection bit
are read.
Initial value of watchdog timer
By a reset or writing to the watchdog timer control register (address
0039
16
), the watchdog timer H is set to “FF
16
” and the watchdog
timer L is set to “FF
16
”.
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 0039
16
). When this bit is
“0”, the count source becomes a watchdog timer L underflow signal.
The detection time is 131.072 ms at f(X
IN
)=8 MHz.
When this bit is “1”, the count source becomes f(X
IN
)/16. In this
case, the detection time is 512 μs at f(X
IN
)=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 (address
0039
16
).
When this bit is “0”, the STP instruction is enabled.
When this bit is “1”, the STP instruction is disabled, and an internal
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
X
IN
Data bus
“0”
“1”
Watchdog timer H count
source selection bit
1/16
Reset
circuit
STP Instruction Disable Bit
STP Instruction
Watchdog timer H (8)
Write "FF
16
" to the
watchdog timer
control register
Internal reset
RESET
Watchdog timer L (8)
Write “FF
16
” to the
watchdog timer
control register
Watchdog timer control register
(WDTCON: address 0039
16
, initial value: 3F
16
)
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(X
IN
)/16
b7 b0
相關(guān)PDF資料
PDF描述
M37534 Single Chip 8 Bits CMOS Microcomputer(8位單片機)
M37700 16-Bit Single-Chip Microcomputer(16位單片微控制器)
M37721 16-Bit Single-Chip Microcomputer(16位單片微控制器)
M37733MHB Single Chip 16 Bits CMOS Microcomputer(16位單片機)
M37735S4L Single Chip 16 Bits CMOS Microcomputer(16位單片機)
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