TMP91C824
91C824-191
3.12.2 Control
registers
The watchdog timer WDT is controlled by two control registers WDMOD and WDCR.
(1) Watch dog timer Mode Register (WDMOD)
!
Setting the detection time for the watch dog timer in <WDTP1,WDTP0>
This 2-bit register is used for setting the watch dog timer interrupt time used when detecting
runaway. After Reset, this register is initialized to WDMOD<WDTP1,WDTP0> = “00”.
The detection times for WDT are shown in Figure 3.12.4.
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Watch dog timer Enable/Disable Control Register <WDTE>
After Reset, WDMOD<WDTE> is initialized to “1”, enabling the watch dog timer.
To disable the watch dog timer, it is necessary to set this bit to “0” and to write the disable code
(B1H) to the watch dog timer Control Register WDCR. This makes it difficult for the watch dog
timer to be disabled by runaway.
However, it is possible to return the watch dog timer from the disabled state to the enabled state
merely by setting <WDTE> to “1”.
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Watch dog timer out reset connection <RESCR>
This register is used to connect the output of the watch dog timer with the RESET terminal
internally. Since WDMOD<RESCR>is initialized to “0” on Reset, a Reset by the watch dog timer
will not be performed.
(2) Watch dog timer Control Register (WDCR)
This register is used to disable and clear the binary counter for the watch dog timer.
Disable control the watch dog timer can be disabled by clearing WDMOD<WDTE> to “0” and
then writing the disable code (B1H) to the WDCR register.
WDMOD
←
0 -
- - - - X X
Clear
WDMOD<WDTE>to
“0”.
WDCR
←
1 0 1 1 0 0 0 1
Write the disable code (B1H).
•
Enable control
Set WDMOD<WDTE>to “1”.
•
Watch dog timer clear control
To clear the binary counter and cause counting to resume, write the clear code (4EH) to the
WDCR register.
WDCR
←
0 1 0 0 1 1 1 0
Write the clear code (4EH).