Z8F640x/Z8F480x/Z8F320x/Z8F240x/Z8F160x
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75
Watch-Dog Timer Control Register Definitions
Watch-Dog Timer Control Register
The Watch-Dog Timer Control (WDTCTL) register, detailed in Table 46, is a Read-Only
register that indicates the source of the most recent Reset event, indicates a Stop Mode
Recovery event, and indicates a Watch-Dog Timer time-out. Reading this register resets
the upper four bits to 0.
Writing the 55H, AAHunlock sequence to the Watch-Dog Timer Control (WDTCTL) reg-
ister address unlocks the three Watch-Dog Timer Reload Byte registers (WDTU, WDTH,
and WDTL) to allow changes to the time-out period. These write operations to the
WDTCTL register address produce no effect on the bits in the WDTCTL register. The
locking mechanism prevents spurious writes to the Reload registers.
Table 46. Watch-Dog Timer Control Register (WDTCTL)
BITS
FIELD
RESET
R/W
7
6
5
4
3
2
1
0
POR
STOP
WDT
EXT
Reserved
X
R
X
R
X
R
0
0
0
0
0
R
R
R
R
R
FF0
ADDR
POR—Power-On Reset Indicator
If this bit is set to 1, a Power-On Reset event occurred. This bit is reset to 0 if a WDT time-
out or Stop Mode Recovery occurs. This bit is also reset to 0 when the register is read.
STOP—STOP Mode Recovery Indicator
If this bit is set to 1, a STOP Mode Recovery occurred. If the STOP and WDT bits are both
set to 1, the STOP Mode Recovery occurred due to a WDT time-out. If the STOPbit is 1
and the WDTbit is 0, the STOP Mode Recovery was not caused by a WDT time-out. This
bit is reset by a Power-On Reset or a WDT time-out that occurred while not in STOP
mode. Reading this register also resets this bit.
WDT—Watch-Dog Timer Time-Out Indicator
If this bit is set to 1, a WDT time-out occurred. A Power-On Reset resets this pin. A Stop
Mode Recovery from a change in an input pin also resets this bit. Reading this register
resets this bit.
EXT—External Reset Indicator
If this bit is set to 1, a Reset initiated by the external RESET pin occurred. A Power-On
Reset or a Stop Mode Recovery from a change in an input pin resets this bit. Reading this
register resets this bit.
PS017610-0404
Watch-Dog Timer
ZILOG [ ZILOG, INC. ]
