
R8C/2C Group, R8C/2D Group
13. Watchdog Timer
Rev.2.00
Dec 05, 2007
REJ09B0339-0200
13.2
Count Source Protection Mode Enabled
The count source of the watchdog timer is the low-speed on-chip oscillator clock when count source protection
mode is enabled. If the CPU clock stops when a program is out of control, the clock can still be supplied to the
watchdog timer.
NOTES:
1. The WDTON bit cannot be changed by a program. To set the WDTON bit, write 0 to bit 0 of address
0FFFFh with a flash programmer.
2. Even if 0 is written to the CSPROINI bit in the OFS register, the CSPRO bit is set to 1. The
CSPROINI bit cannot be changed by a program. To set the CSPROINI bit, write 0 to bit 7 of address
0FFFFh with a flash programmer.
Table 13.3
Watchdog Timer Specifications (with Count Source Protection Mode Enabled)
Item
Specification
Count source
Low-speed on-chip oscillator clock
Count operation
Decrement
Period
Count value of watchdog timer (4096)
Low-speed on-chip oscillator clock
Example: Period is approximately 32.8 ms when the low-speed on-
chip oscillator clock frequency is 125 kHz
Reset condition of watchdog
timer
Reset
Write 00h to the WDTR register before writing FFh
Underflow
Count start condition
The WDTON bit(1) in the OFS register (0FFFFh) selects the operation
of the watchdog timer after a reset.
When the WDTON bit is set to 1 (watchdog timer is in stop state
after reset)
The watchdog timer and prescaler stop after a reset and the count
starts when the WDTS register is written to
When the WDTON bit is set to 0 (watchdog timer starts
automatically after reset)
The watchdog timer and prescaler start counting automatically after
a reset
Count stop condition
None (The count does not stop in wait mode after the count starts.
The MCU does not enter stop mode.)
Operation at time of underflow
Registers, bits
When setting the CSPPRO bit in the CSPR register to 1 (count
source protection mode is enabled)(2), the following are set
automatically
- Set 0FFFh to the watchdog timer
- Set the CM14 bit in the CM1 register to 0 (low-speed on-chip
oscillator on)
- Set the PM12 bit in the PM1 register to 1 (The watchdog timer is
reset when watchdog timer underflows)
The following conditions apply in count source protection mode
- Writing to the CM10 bit in the CM1 register is disabled (It remains
unchanged even if it is set to 1. The MCU does not enter stop
mode.)
- Writing to the CM14 bit in the CM1 register is disabled (It remains
unchanged even if it is set to 1. The low-speed on-chip oscillator
does not stop.)