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Rev.1.02 Jul 01, 2005 page 77 of 314
REJ09B0126-0102
M16C/6N Group (M16C/6NL, M16C/6NN) 10. Watchdog Timer
Under development
This document is under development and its contents are subject to change.
Figure 10.2 WDC Register and WDTS Register
10.1 Count Source Protective Mode
In this mode, a on-chip oscillator clock is used for the watchdog timer count source. The watchdog timer
can be kept being clocked even when CPU clock stops as a result of runaway.
Before this mode can be used, the following register settings are required:
(1) Set the PRC1 bit in the PRCR register to “1” (enable writes to the PM1 and PM2 registers).
(2) Set the PM12 bit in the PM1 register to “1” (reset when the watchdog timer underflows).
(3) Set the PM22 bit in the PM2 register to “1” (on-chip oscillator clock used for the watchdog timer count source).
(4) Set the PRC1 bit in the PRCR register to “0” (disable writes to the PM1 and PM2 registers).
(5) Write to the WDTS register (watchdog timer starts counting).
Setting the PM22 bit to “1” results in the following conditions:
• The on-chip oscillator starts oscillating, and the on-chip oscillator clock becomes the watchdog timer
count source.
• The CM10 bit in the CM1 register is disabled against write. (Writing a “1” has no effect, nor is stop mode entered.)
• The watchdog timer does not stop when in wait mode or hold state.
High-order Bit of Watchdog Timer
Prescaler Select Bit
0 : Divided by 16
1 : Divided by 128
Reserved Bit Set to "0"
WDC7
Watchdog Timer Control Register
b7 b6 b5 b4 b3 b2 b1 b0
00
RW
RO
RW
RW
-
(b4-b0)
-
(b6-b5)
FunctionBit Symbol
Bit Name
Symbol Address After Reset
WDC 000Fh 00XXXXXXb
The watchdog timer is initialized and starts counting after a write instruction to
this register. The watchdog timer value is always initialized to "7FFFh" regardless
of whatever value is written.
Watchdog Timer Start Register
(1)
Symbol Address After Reset
WDTS 000Eh Indeterminate
Function
RW
b7 b0
WO
NOTE
1. Write to the WDTS register after the watchdog timer interrupt request is generated.
Watchdog timer count (32768)
on-chip oscillator clock
Watchdog timer period =