361
Chapter 12
Watchdog Timer Function
Preliminary User’s Manual U15839EE1V0UM00
(3)
Watchdog timer command register (WCMD)
This command register WCMD is used to protect the WDTM register from unintended writing.
Writing to WDTM register is possible only immediately after writing to WCMD register. Data written
into WCMD register are ignored. Data read from WCMD register are undefined, too.
WDTM is set by an 8-bit memory manipulation instruction.
Caution:
WCMD register setting by DMA transfer is prohibited. This registers should be writ-
ten with STORE instruction execution by CPU only.
Figure 12-4:
Watchdog Timer Mode Register (WCMD)
(4)
Watchdog timer command status register (WPHS)
The WPHS register monitors the success of a write instruction to the WDTM register. If the write to
WDTM fails because of violating the special instruction sequence writing WCMD immediately
before WDTM, the WPRERR flag is set.
WPHS can be accessed by 8-bit or 1-bit memory instructions.
Caution:
The WPERR bit can only be reset by software. Setting the WPERR by software is not
possible.
Figure 12-5:
Watchdog Timer Mode Register (WPHS)
7
6
5
4
3
2
1
0
Address
R/W
After reset
WCMD
X
X
X
X
X
X
X
X
FFFF F580H
R/W
undefined
7
6
5
4
3
2
1
0
Address
R/W
After reset
WPHS
0
0
0
0
0
0
0
WPRERR FFFF F582H R/W
00H
WPRERR
WDTM register Protection Error Flag
0
no WDTM register writing error has occurred
1
an WDTM register writing error has occurred
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