參數資料
型號： M38039FFSP
廠商： Mitsubishi Electric Corporation
英文描述： SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
中文描述： 單芯片8位CMOS微機
文件頁數： 69/135頁
文件大?。?/td> 2055K
代理商： M38039FFSP
69
3803/3804 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
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, be-
cause 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 “FF
16
” and watchdog timer H is set to
“FF
16
” by writing to the watchdog timer control register (address
001E
16
) or at a reset. Any write instruction that causes a write sig-
nal 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.
Watchdog Timer Operations
The watchdog timer stops at reset and a countdown is started by
the writing to the watchdog timer control register. An internal reset
occurs when watchdog timer H underflows. The reset is released
after its release time. After the release, the program is restarted
from the reset vector address. Usually, write to the watchdog timer
control register by software before an underflow of the watchdog
timer H. The watchdog timer does not function if the watchdog
timer control register is not written to at least once.
Fig. 63 Structure of Watchdog timer control register
When bit 6 of the watchdog timer control register is kept at “0”, the
STP instruction is enabled. When that is executed, both the clock
and the watchdog timer stop. Count re-starts at the same time as
the release of stop mode
(Note)
. The watchdog timer does not
stop while a WIT instruction is executed. In addition, the STP in-
struction is disabled by writing “1” to this bit again. When the STP
instruction is executed at this time, it is processed as an undefined
instruction, and an internal reset occurs. Once a “1” is written to
this bit, it cannot be programmed to “0” again.
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 X
CIN
= 32.768 kHz; 32 s
when X
IN
= 16 MHz; 65.536 ms
Bit 7 of the watchdog timer control register is “1”:
when X
CIN
= 32.768 kHz; 125 ms
when X
IN
= 16 MHz; 256
μ
s
Note:
The watchdog timer continues to count even while waiting for a stop
release. Therefore, make sure that watchdog timer H does not un-
derflow during this period.
Fig. 62 Block diagram of Watchdog timer
X
IN
Data bus
X
CIN
“
10
”
“
00
”
“
01
”
Main clock division
ratio selection bits
(Note)
“
0
”
“
1
”
1/16
Watchdog timer H count
source selection bit
Reset
circuit
STP instruction disable bit
STP instruction
Watchdog timer H (8)
“
FF
16
”
is set when
watchdog timer
control register is
written to.
Internal reset
RESET
Watchdog timer L (8)
Note:
Either high-speed, middle-speed or low-speed mode is selected by bits 7 and 6 of the CPU mode register.
“
FF
16
”
is set when
watchdog timer
control register is
written to.
Reset release time waiting
b7
Watchdog timer H (for read-out of 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 or f(X
CIN
)/16
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