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Chapter 12
Watchdog Timer Function
Preliminary User’s Manual U15839EE1V0UM00
(2)
Watchdog timer mode register (WDTM)
This register sets the operating mode of the watchdog timer, and enables and disables counting.
Data can be written to it only in a sequence of specific instructions so that its contents are not eas-
ily rewritten in case of program hang-up. See also WCMD register.
Once the watchdog timer is started (RUN = 1) after reset, this register cannot be changed.
WDTM is set by an 8/1-bit memory manipulation instruction.
Cautions: 1. The WDTM4 bit has to set to “1” at the initialisation of the WDT
2. WDTM register setting by DMA transfer is prohibited. This registers should be
written with STORE instruction execution by CPU only.
Figure 12-3:
Watchdog Timer Mode Register (WDTM)
Notes: 1. If RUN is set to “1” once, the register cannot be cleared to “0” by software. Therefore, when
the count starts, the count cannot be stopped except by RESET input.
2. The WDTM4 bit has to set to “1” at the initialisation of the WDT.
Cautions: 1. Data is set to the CKC register by the following sequence:
•
Write any 8-bit data to the command register (WCMD)
•
Write the set data to the destination register (WDTM)
2. If RUN is set to “1” and the watchdog timer is cleared, the actual overflow time
may be up to 2
12
/f
XX
seconds less than the set time.
7
6
5
4
3
2
1
0
Address
R/W
After reset
WDTM
RUN
0
0
WDTM4 WDTM3
0
0
0
FFFF F572H
R/W
00H
RUN
Operating Mode Selection for the Watchdog Timer
Note 1
0
After Reset: disable count (writing during counting: clear old count)
1
After Reset: start counting (writing during counting: clear old count)
WDTM4
Note 2
WDTM3
Watchdog Timer Operation Mode Selection
1
0
Watchdog timer mode 1
(Non-maskable interrupt occurs upon generation of an overflow)
1
1
Watchdog timer mode 2
(RESET operation is activated upon generation of an overflow)
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