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參數(shù)資料
| 型號： | M37542F8SP |
| 元件分類： | 微控制器/微處理器 |
| 英文描述： | 8-BIT, FLASH, 8 MHz, MICROCONTROLLER, PDIP32 |
| 封裝： | 8.9 X 28 MM, 1.78 MM PITCH, PLASTIC, SDIP-32 |
| 文件頁數(shù)： | 82/124頁 |
| 文件大?。?/td> | 1238K |
| 代理商： | M37542F8SP |
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7542 Group
Rev.3.03
Jul 11, 2008
Page 58 of 117
REJ03B0006-0303
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 function selection 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 (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 function selection bit
When “0” is set to STP instruction function selection bit, system
enters into the stop mode at the STP instruction execution.
When “1” is set to this bit, internal reset occurs at the STP instruc-
tion execution.
This bit is set to “1” by program, but it cannot be changed to “0” .
This bit is cleared to “0” after reset.
■ Notes on Watchdog Timer
1. The watchdog timer is operating during the wait mode. Write data
to the watchdog timer control register to prevent timer underflow.
2. The watchdog timer stops during the stop mode. However, the
watchdog timer is running during the oscillation stabilizing time
after the STP instruction is released. In order to avoid the under-
flow of the watchdog timer, the watchdog timer control register
must be written just before executing the STP instruction.
3. The STP instruction function selection bit (bit 6 of watchdog
timer control register (address 003916)) can be rewritten only
once after releasing reset. After rewriting it is disable to write
any data to this bit.
4. A count source of watchdog timer is affected by the clock divi-
sion selection bit of the CPU mode register.
The f(XIN) clock is supplied to the watchdog timer when select-
ing f(XIN) as the CPU clock.
The on-chip oscillator output is supplied to the watchdog timer
when selecting the on-chip oscillator output as the CPU clock.
Fig. 71 Block diagram of watchdog timer
Fig. 72 Structure of 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 function selection bit
0 : System enters into the stop mode
at the STP instruction execution
1 : Internal reset occurs at the STP instruction execution
Watchdog timer H count source selection bit
0 : Watchdog timer L underflow
1 : f(XIN)/16 or on-chip oscillator/16
b7
b0
XIN clock
On-chip oscillator
Source clock selection
(auto-switch depending on setting of CPUM)
Data bus
“0”
“1”
1/16
Watchdog timer H count
source selection bit
Reset
circuit
STP Instruction function selection 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
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| M37542F8SP#U0 | 制造商:Renesas Electronics Corporation 功能描述:MCU 4.0/5.5V 32K PB-FREE 32-SDIP - Trays |
| M37542M2-XXXFP | 制造商:RENESAS 制造商全稱:Renesas Technology Corp 功能描述:SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER |
| M37542M2-XXXGP | 制造商:RENESAS 制造商全稱:Renesas Technology Corp 功能描述:SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER |
| M37542M2-XXXHP | 制造商:RENESAS 制造商全稱:Renesas Technology Corp 功能描述:SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER |
| M37542M2-XXXSP | 制造商:RENESAS 制造商全稱:Renesas Technology Corp 功能描述:SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER |
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