
R8C/3GM Group
14. Watchdog Timer
R01UH0284EJ0100 Rev.1.00
Aug 09, 2011
14.3.3
Count Source Protection Mode Enabled
The count source for the watchdog timer is the low-speed on-chip oscillator clock for the watchdog timer 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 this 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 this bit, write 0 to bit 7 of address 0FFFFh
with a flash programmer.
3. Write the WDTR register during the count operation of the watchdog timer.
Table 14.3
Watchdog Timer Specifications (Count Source Protection Mode Enabled)
Item
Specification
Count source
Low-speed on-chip oscillator clock
Count operation
Decrement
Period
Count value of watchdog timer (m)
Low-speed on-chip oscillator clock for the watchdog timer
m: Value set by bits WDTUFS0 and WDTUFS1 in the OFS2 register
Example:
The period is approximately 8.2 ms when:
- The on-chip oscillator clock for the watchdog timer is set to 125 kHz.
- Bits WDTUFS1 to WDTUFS0 are set to 00b (03FFh).
Watchdog timer
initialization conditions
Reset
Write 00h and then FFh to the WDTR register.
(3) Underflow
Count start conditions
The operation of the watchdog timer after a reset is selected by
the WDTON bit
(1) in the OFS register (address 0FFFFh).
When the WDTON bit is set to 1 (watchdog timer is stopped after reset).
The watchdog timer and prescaler are stopped after a reset and
start counting 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 (Count does not stop even in wait mode and stop mode once it starts.)
Operation at underflow
Registers, bits
When the CSPPRO bit in the CSPR register is set to 1 (count source
protection mode enabled)
(2), the following are set automatically:
- The low-speed on-chip oscillator for the watchdog timer is on.
- The PM12 bit in the PM1 register is set to 1 (watchdog timer reset when the
watchdog timer underflows).