CHAPTER 9 WATCHDOG TIMER
Preliminary User’s Manual U16846EJ1V0UD
173
Table 9-2. Option Byte Setting and Watchdog Timer Operation Mode
Option Byte
Ring-OSC Cannot Be Stopped
Ring-OSC Can Be Stopped by Software
Watchdog timer clock
source
Fixed to f
R
Note 1
.
•
Selectable by software (f
XP
, f
R
or
stopped)
•
When reset is released: f
R
Operation after reset
Operation starts with the maximum
interval (f
R
/2
18
).
Operation starts with maximum
interval (f
R
/2
18
).
Operation mode selection
The interval can be changed only
once.
The clock selection/interval can be
changed only once.
Features
The watchdog timer cannot be
stopped.
The watchdog timer can be stopped in
standby mode
Note 2
.
Notes 1. As long as power is being supplied, Ring-OSC oscillation cannot be stopped (except in the reset
period).
2. The conditions under which clock supply to the watchdog timer is stopped differ depending on
the clock source of the watchdog timer.
<1> If the clock source is f
XP
, clock supply to the watchdog timer is stopped under the following
conditions.
•
When f
XP
is stopped
•
In HALT/STOP mode
•
During oscillation stabilization time
<2> If the clock source is f
R
, clock supply to the watchdog timer is stopped under the following
conditions.
•
If the CPU clock is f
XP
and if f
R
is stopped by software before execution of the STOP
instruction
•
In HALT/STOP mode
Remarks 1. f
R
: Ring-OSC clock oscillation frequency
2. f
XP
: High-speed system clock oscillation frequency
