m37702s1afp Mitsumi Electronics, Corp., m37702s1afp Datasheet - Page 36

• Manufacturer Part Number: m37702s1afp
• Description: Single-chip 16-bit Cmos Microcomputer
• Manufacturer: Mitsumi Electronics, Corp.

WATCHDOG TIMER
The watchdog timer is used to detect unexpected execution se-
quence caused by software run-away.
Figure 46 shows a block diagram of the watchdog timer. The
watchdog timer consists of a 12-bit binary counter.
The watchdog timer counts the clock frequency divided by 32 (f
or by 512 (f
watchdog timer frequency selection flag shown in Figure 47. f
is selected when the flag is “0” and f
The flag is cleared after reset. FFF
when “L” or 2V
executed, data is written to the watchdog timer, or the most signifi-
cant bit of the watchdog timer become “0”.
After FFF
timer is decremented by one at every cycle of selected frequency
f
dog timer become “0”, and a watchdog timer interrupt request bit
is set, and FFF
Normally, a program is written so that data is written in the watch-
dog timer before the most significant bit of the watchdog timer
become “0”. If this routine is not executed due to unexpected pro-
gram execution, the most significant bit of the watchdog timer
become eventually “0” and an interrupt is generated.
The processor can be reset by setting the bit 3 (software reset bit)
of processor mode register described in Figure 10 in the interrupt
section and generating a reset pulse.
The watchdog timer stops its function when the RESET pin volt-
age is raised to double the V
The watchdog timer can also be used to recover from when the
clock is stopped by the STP instruction. Refer to the section on
clock generation circuit for more details.
The watchdog timer hold the contents during a hold state and the
frequency is stopped to input.
36
32
or f
512
16
, and after 2048 counts, the most significant bit of watch-
512
is set in the watchdog timer, the contents of watchdog
). Whether to count f
CC
16
is preset in the watchdog timer.
is applied to the RESET pin, STP instruction is
CC
voltage.
16
______
32
32
is set in the watchdog timer
or f
is selected when it is “1”.
512
is determined by the
______
M37702M2AXXXFP, M37702M2BXXXFP
512
32
)
Fig. 46 Watchdog timer block diagram
Fig. 47 Watchdog timer frequency selection flag
M37702S1AFP, M37702S1BFP
STP instruction
RESET
7
Watchdog timer
frequency selection (connection forced to f
6
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Write to watchdog
5
4
detection
circuit
2Vcc
S
R
3
f
f
MITSUBISHI MICROCOMPUTERS
32
512
Hold
Q
timer
2
1
0
STP instruction execution)
Watchdog timer
frequency selection
0 : Select f
1 : Select f
Watchdog timer
(60
16
)
32
512
32
during
Set “FFF
Address
61
16
16
”