M16C Datasheet, PDF (79/262 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Preliminary Specifications REV.B
Mitsubishi microcomputers
Specifications in this manual are tentative and subject to change.
M16C / 6N Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Watchdog Timer
Watchdog Timer
The watchdog timer has the function of detecting when the program is out of control. The watchdog timer is
a 15-bit counter which down-counts the clock derived by dividing the internal clock φ using the prescaler. A
watchdog timer interrupt is generated when an underflow occurs in the watchdog timer. When XIN is se-
lected for the internal clock φ, bit 7 of the watchdog timer control register (address 000F16) selects the
prescaler division ratio (by 16 or by 128). When XCIN is selected as the internal clock φ, the prescaler is set
for division by 2 regardless of bit 7 of the watchdog timer control register (address 000F16). Table 8-1 shows
the periodic table for the watchdog timer.
Table 8-1. Watchdog timer periodic table (XIN = 10MHz, XCIN = 32kHz)
CM07
0
CM06
0
CM17 CM16
0
0
Internal clock φ
10MHz
0
0
0
1
5MHz
0
0
1
0
2.5MHz
0
0
1
1
0.625MHz
0
1
Invalid Invalid
1.25MHz
1
Invalid Invalid Invalid
Note: Error is generated by the prescaler.
32kHz
WDC7
0
1
0
1
0
1
0
1
0
1
Invalid
Period
Approx. 52.4ms (Note)
Approx. 419.2ms (Note)
Approx. 104.9ms (Note)
Approx. 838.8ms (Note)
Approx. 209.7ms (Note)
Approx. 1.68s (Note)
Approx. 838.8ms (Note)
Approx. 6.71s (Note)
Approx. 419.2ms (Note)
Approx. 3.35s (Note)
Approx. 2s (Note)
The watchdog timer is initialized by writing to the watchdog timer start register (address 000E16) and when a
watchdog timer interrupt request is generated. The prescaler is initialized only when the microcomputer is
reset. After a reset is cancelled, the watchdog timer and prescaler are both stopped. The count is started by
writing to the watchdog timer start register (address 000E16).
Figure 8-1 shows the block diagram of the watchdog timer. Figure 8-2 shows the watchdog timer-related
registers.
Internal clock
HOLD
Write to the watchdog timer
start register
(address 000E16)
RESET
Prescaler
1/16
“CM07 = 0”
“WDC7 = 0”
1/128
“CM07 = 0”
“WDC7 = 1”
“CM07 = 1”
1/2
Watchdog timer
Set to
“7FFF16”
Watchdog timer
interrupt request
Figure 8-1. Block diagram of watchdog timer
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