R8C/1A Group, R8C/1B Group 13. Watchdog Timer
Rev.1.30 Dec 08, 2006 Page 103 of 315
REJ09B0252-0130
13. Watchdog Timer
The watchdog timer is a function that detects when a program is out of control. Use of the watchdog timer is
recommended to improve the reliability of the system. The watchdog timer contains a 15-bit counter and allows
selection of count source protection mode enable or disable. Table 13.1 lists information on the Count Source
Protection Mode.
Refer to 6.5 Watchdog Timer Reset for details on the watchdog timer reset.
Figure 13.1 shows the Block Diagram of Watchdog Timer and Figures 13.2 to 13.3 show Registers OFS, WDC,
WDTR, WDTS, and CSPR.
Figure 13.1 Block Diagram of Watchdog Timer
Table 13.1 Count Source Protection Mode
Item
Count Source Protection Mode
Disabled
Count Source Protection Mode
Enabled
Count source CPU clock Low-speed on-chip oscillator
clock
Count operation Decrement
Reset condition of watchdog
timer
• Reset
• Write 00h to the WDTR register before writing FFh
• underflow
Count start condition Either of the following can be selected
• After reset, count starts automatically
• Count starts by writing to WDTS register
Count stop condition Stop mode, wait mode None
Operation at time of underflow Watchdog timer interrupt or
watchdog timer reset
Watchdog timer reset
CPU clock
1/16
1/128
Watchdog timer
Internal
reset signal
Write to WDTR register
WDC7 = 0
WDC7 = 1
Set to
7FFFh
(1)
PM12 = 1
Watchdog
timer reset
PM12 = 0
Watchdog timer
interrupt request
Prescaler
CSPRO = 0
fRING-S
CSPRO = 1
CSPRO: Bit in CSPR register
WDC7: Bit in WDC register
PM12: Bit in PM1 register
NOTE:
1. When the CSPRO bit is set to 1 (count source protection mode enabled), 0FFFh is set.
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