CHAPTER 9 WATCHDOG TIMER
Preliminary User’s Manual U16846EJ1V0UD
174
9.2 Configuration of Watchdog Timer
The watchdog timer includes the following hardware.
Table 9-3. Configuration of Watchdog Timer
Item Configuration
Control registers
Watchdog timer mode register (WDTM)
Watchdog timer enable register (WDTE)
Figure 9-1. Block Diagram of Watchdog Timer
f
R
/2
2
Clock
input
controller
Output
controller
Internal reset signal
WDCS2
Internal bus
WDCS1 WDCS0
f
XP
/2
4
WDCS3
WDCS4
0
1
1
Selector
16-bit
counter
or
f
XP
/2
13
to
f
XP
/2
20
f
R
/2
11
to
f
R
/2
18
Watchdog timer enable
register (WDTE)
Watchdog timer mode
register (WDTM)
3
3
2
Clear
Option byte
(to set “Ring-OSC
cannot be stopped” or
“Ring-OSC can be
stopped by software”)
9.3 Registers Controlling Watchdog Timer
The watchdog timer is controlled by the following two registers.
•
Watchdog timer mode register (WDTM)
•
Watchdog timer enable register (WDTE)
(1) Watchdog timer mode register (WDTM)
This register sets the overflow time and operation clock of the watchdog timer.
This register can be set by an 8-bit memory manipulation instruction and can be read many times, but can be
written only once after reset is released.
RESET input sets this register to 67H.