CHAPTER 9 WATCHDOG TIMER
179
User’s Manual U11302EJ4V0UM
(2) Watchdog timer mode register (WDTM)
This register sets the watchdog timer operating mode and enables/disables counting.
WDTM is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input sets WDTM to 00H.
Figure 9-3. Format of Watchdog Timer Mode Register
Notes 1.
Once set to 1, WDTM3 and WDTM4 cannot be cleared to 0 by software.
2.
Starts operation as an interval timer as soon as RUN is set to 1.
3.
Once set to 1, RUN cannot be cleared to 0 by software. Thus, once counting starts, it can only
be stopped by RESET input.
Cautions 1. When RUN is set to 1 so that the watchdog timer is cleared, the actual overflow time
is up to 0.5% shorter than the time set by timer clock select register 2 (TCL2).
2. When using watchdog timer mode 1 and 2, make sure that the interrupt request flag
(TMIF4) is set to 0 before setting WDTM4 to 1. If WDTM4 is set to 1 while TMIF4 is 1,
a non-maskable interrupt request occurs regardless of the contents of WDTM3.
Remark
x: don’t care
<7>
6
5
4
3
2
1
0
RUN
0
0
WDTM4 WDTM3
0
0
0
Symbol
WDTM
Address
FFF9H
After reset
00H
R/W
R/W
WDTM4
0
1
1
Watchdog timer operating mode selection
Note 1
Interval timer mode
Note 2
(Maskable interrupt request occurs upon
generation of an overflow.)
Watchdog timer mode 1
(Non-maskable interrupt request occurs
upon generation of an overflow.)
Watchdog timer mode 2
(Reset operation is activated upon
generation of an overflow.)
RUN
0
1
Watchdog timer operation selection
Note 3
Count stop
Counter is cleared and counting starts.
WDTM3
x
0
1
Содержание mPD780204
Страница 2: ...2 User s Manual U11302EJ4V0UM MEMO ...