
Watchdog Timer
96
Mitsubishi microcomputers
M16C / 62P Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Under
development
Preliminary Specifications Rev.1.0
Specifications in this manual are tentative and subject to change.
Watchdog timer start register (Note)
Symbol
Address
After reset
WDTS
000E16
Indeterminate
WO
b7
b0
Function
The watchdog timer is initialized and starts counting after a write instruction to
this register. The watchdog timer value is always initialized to “7FFF16”
regardless of whatever value is written.
RW
Note : Write to the WDTS register after the watchdog timer interrupt occurs.
Figure 1.12.2. WDC Register and WDTS Register
CPU
clock
Write to WDTS register
RESET
PM12 = 0
Watchdog timer
Set to
“7FFF16”
1/128
1/16
CM07 = 0
WDC7 = 1
CM07 = 0
WDC7 = 0
CM07 = 1
HOLD
1/2
Prescaler
PM12 = 1
Watchdog timer
interrupt request
Reset
PM22 = 0
PM22 = 1
Ring oscillator clock
Figure 1.12.1. Watchdog Timer Block Diagram
Watchdog timer control register
Symbol
Address
After reset
WDC
000F16
00XXXXXX2(Note2)
Function
Bit symbol
RW
b7
b6
b5
b4
b3
b2
b1
b0
High-order bit of watchdog timer
WDC7
Bit name
Prescaler select bit
0 : Divided by 16
1 : Divided by 128
Reserved bit
Must set to “0”
0
RO
RW
Cold start / warm start
discrimination flag (Note 1)
0 : Cold start
1 : Warm start
WDC5
Note 1: The WDC5 bit is always “1” (warm start) no matter how it is set by writing a “0” or “1”.
Note 2: The WDC5 bit is “0” (cold start) immediately after power-on. It can only be set to “1” in a program. It is set
to “0” when the input voltage at the VCC1 pin drops to Vdet2 or less while the VC25 bit in the VCR2 register
is set to “1” (RAM retention limit detection circuit enable).
(b4-b0)
(b6)
Setting the PM22 bit to “1” results in the following conditions
The ring oscillator starts oscillating, and the ring oscillator clock becomes the watchdog timer count
source.
The CM10 bit of 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.