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參數(shù)資料
| 型號： | M38049FFLSP |
| 元件分類： | 微控制器/微處理器 |
| 英文描述： | 8-BIT, FLASH, 16.8 MHz, MICROCONTROLLER, PDIP64 |
| 封裝： | 17 X 56.40 MM, 1.78 MM HEIGHT, PLASTIC, SDIP-64 |
| 文件頁數(shù)： | 89/129頁 |
| 文件大小： | 1721K |
| 代理商： | M38049FFLSP |
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Rev.1.00
Oct 27, 2008
Page 62 of 128
REJ03B0266-0100
3804 Group (Spec.L)
WATCHDOG TIMER
The watchdog timer gives a mean of returning to the reset status
when a program cannot run on a normal loop (for example,
because of a software run-away). The watchdog timer consists of
an 8-bit watchdog timer L and an 8-bit watchdog timer H.
Watchdog Timer Initial Value
Watchdog timer L is set to “FF16” and watchdog timer H is set to
“FF16” by writing to the watchdog timer control register (address
001E16) or at a reset. Any write instruction that causes a write
signal can be used, such as the STA, LDM, CLB, etc. Data can
only be written to bits 6 and 7 of the watchdog timer control
register. Regardless of the value written to bits 0 to 5, the above-
mentioned value will be set to each timer.
Bit 6 can be written only once after releasing reset. After
rewriting it is disable to write any data to this bit.
Watchdog Timer Operations
The watchdog timer stops at reset and starts to count down by
writing to the watchdog timer control register (address 001E16).
An internal reset occurs at an underflow of the watchdog timer
H. The reset is released after waiting for a reset release time and
the program is processed from the reset vector address.
Accordingly, programming is usually performed so that writing
to the watchdog timer control register may be started before an
underflow. If writing to the watchdog timer control register is not
performed once, the watchdog timer does not function.
Bit 6 of Watchdog Timer Control Register
When bit 6 of the watchdog timer control register is “0”, the
MCU enters the stop mode by execution of STP instruction.
Just after releasing the stop mode, the watchdog timer restarts
counting(Note.). When executing the WIT instruction, the
watchdog timer does not stop.
When bit 6 is “1”, execution of STP instruction causes an
internal reset. When this bit is set to “1” once, it cannot be
rewritten to “0” by program. Bit 6 is “0” at reset.
The following shows the period between the write execution to
the watchdog timer control register and the underflow of
watchdog timer H.
Bit 7 of the watchdog timer control register is “0”:
when XCIN = 32.768 kHz; 32 s
when XIN = 16 MHz; 65.536 ms
Bit 7 of the watchdog timer control register is “1”:
when XCIN = 32.768 kHz; 125 ms
when XIN = 16 MHz; 256
μs
Note. The watchdog timer continues to count even during the wait time
set by timer 1 and timer 2 to release the stop state and in the wait
mode. Accordingly, write to the watchdog timer control register to
not underflow the watchdog timer in this time.
Fig. 58 Block diagram of Watchdog timer
Fig. 59 Structure of Watchdog timer control register
XIN
Data bus
XCIN
“10”
“00”
“01”
Main clock division
ratio selection bits(1)
“0”
“1”
1/16
Watchdog timer H count
source selection bit
Reset
circuit
STP instruction function selection bit
Watchdog timer H (8)
“FF16” is set when
watchdog timer
control register is
written to.
Internal reset
Watchdog timer L (8)
“FF16” is set when
watchdog timer
control register is
written to.
Note 1: Any one of high-speed, middle-speed or low-speed mode is selected by bits 7 and 6 of the CPU mode register.
STP instruction
RESET
b7
Watchdog timer H (for read-out of high-order 6 bit)
STP instruction function selection bit
0: Entering stop mode by execution of STP instruction
1: Internal reset by execution of STP instruction
Watchdog timer H count source selection bit
0: Watchdog timer L underflow
1: f(XIN)/16 or f(XCIN)/16
Watchdog timer control register
(WDTCON : address 001E16)
b0
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