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參數(shù)資料
| 型號： | M38C2XMX |
| 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(shù)： | 44/63頁 |
| 文件大?。?/td> | 1000K |
| 代理商： | M38C2XMX |
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44
38C2 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
PRELIMINARY
Notice: This is not a final specification.
Some parametric limits are subject to change.
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
counter.
Initial Value of Watchdog Timer
At reset or writing to the watchdog timer control register, each watch-
dog timer is set to
“
FF
16
.
”
Instructions such as STA, LDM and CLB to
generate the write signals can be used.
The written data in bits 0 to 5 are not valid, and the above values are
set.
Standard Operation of Watchdog Timer
The watchdog timer is in the stop state at reset and the watchdog
timer starts to count down by writing an optional value in the watch-
dog timer control register. An internal reset occurs at an underflow of
the watchdog timer. Then, reset is released after the reset release
time is elapsed, the program starts from the reset vector address.
Normally, writing to the watchdog timer control register before an
underflow of the watchdog timer is programmed. If writing to the watch-
dog control register is not executed, the watchdog timer does not
operate.
Fig. 44 Timing diagram of reset output
When reading the watchdog timer control register is executed, the
contents of the high-order 6-bit counter and the STP instruction dis-
able bit (bit 6), and the count source selection bit (bit 7) are read out.
When the STP instruction disable bit is
“
0
”
, the STP instruction is
valid. The STP instruction is disabled by writing to
“
1
”
to this bit. In
this time, when the STP instruction is executed, it is handled as the
undefined instruction, the internal reset occurs. This bit cannot be
cleared to
“
0
”
by program. This bit is
“
0
”
after reset.
The time until the underflow of the watchdog timer control register
after writing to the watchdog timer control register is executed is as
follows (when the bit 7 of the watchdog timer control register is
“
0
”
) ;
at through, frequency/2/4/8 mode (f(X
IN
)) = 8 MHz): 32.768 ms
at low-speed mode (f(X
CIN
) = 32 KHz): 8.19s
I
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, do not underflow the watchdog timer in this time.
Fig. 42 Block diagram of Watchdog timer
Fig. 43 Structure of Watchdog timer control register
b0
STP instruction disable bit
0: STP instruction enabled
1: STP instruction disabled
Watchdog timer count source selection bit
0: 1/1024 of system clock
1: 1/4 of system clock
Watchdog timer H (for read-out of high-order 6 bit)
“
FF
16
”
is set to watchdog timer by writing to these bits.
Watchdog timer control register
(WDTCON : address 0037
16
)
b7
I
s
n
i
t
g
e
n
r
n
a
a
l
l
r
e
s
e
t
Watchdog timer detected
≈
32
msec
(at f(X
IN
)=8MH
Z
)
f
(
X
I
N
)
X
IN
X
C
I
N
Sy
b
i
s
(
t
b
e
m
t
c
)
l
o
c
k
c
o
n
t
r
o
“
0
”
l
t
i
6
1/1024
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s
t
r
u
R
c
e
t
i
s
o
e
n
t
R
E
S
E
T
I
N
Wait until reset release
1
/
4
D
a
t
a
b
u
s
W
c
s
“
0
”
a
u
l
e
t
n
c
h
t
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d
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m
e
r
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o
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t
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c
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t
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o
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d
i
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i
s
s
a
t
r
b
u
l
c
e
t
i
b
o
i
n
t
Watchdog timer
H (6)
Internal reset
T
Watchdog timer
L (2)
“
F
w
c
w
F
1
a
t
o
n
r
i
6
”
h
r
o
e
d
l
n
i
s
o
r
t
g
e
o
s
e
t
g
.
t
m
s
w
e
t
e
h
r
r
e
i
n
c
t
t
i
i
s
t
“
1
”
“
1
”
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