NEC NEC PD78081(A), User Manual

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108
CHAPTER 7 WATCHDOG TIMER
RUM
7
0
6
0 WDTM4
4
WDTM3
3 2 1 0
FFF9H
Address
WDTM
Symbol
0 0 0
5
00H
After
Reset
R/W
R/W
RUN
0
1
Watchdog Timer Operation Mode Selection Note 3
Count stop
Counter is cleared and counting starts.
WDTM3
×
0
1
Watchdog Timer Operation Mode
Selection
Note 1
Interval timer mode
Note 2
(Maskable interrupt occurs upon
generation of an overflow.)
Watchdog timer mode 1
(Non-maskable interrupt occurs upon
generation of an overflow.)
Watchdog timer mode 2
(Reset operation is activated upon
generation of an overflow.)
WDTM4
0
1
1
(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 7-3. Watchdog Timer Mode Register Format
Notes 1. Once set to 1, WDTM3 and WDTM4 cannot be cleared to 0 by software.
2. The watchdog timer starts operating as an interval timer as soon as RUN has been 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 1 is set in RUN 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.
2. To use watchdog timer modes 1 and 2, make sure that the interrupt request flag (TMIF4)
is 0, and then set WDTM4 to 1.
If WDTM4 is set to 1 when TMIF4 is 1, the non-maskable interrupt request occurs,
regardless of the contents of WDTM3.
Remark
×
: Don’t care