µ
PD754144, 754244
36
Data Sheet U10040EJ2V1DS
10.2 Watchdog Flag (WDF), Key Return Flag (KRF)
The WDF is cleared by a watchdog timer overflow signal, and the KRF is set by a reset signal generated by
the KRn pins. As a result, by checking the contents of WDF and KRF, it is possible to know what kind of reset
signal is generated.
As the WDF and KRF are cleared only by external signal or instruction execution, if once these flags are set,
they are not cleared until an external signal is generated or a clear instruction is executed. Check and clear the
contents of WDF and KRF after reset start operation by executing SKTCLR instruction and so on.
Table 10-2 lists the contents of WDF and KRF corresponding to each signal. Figure 10-3 shows the WDF
operation in generating each signal, and Figure 10-4 shows the KRF operation in generating each signal.
Table 10-2. WDF and KRF Contents Correspond to Each Signal
External RESET
Reset signal
Reset signal
WDF clear
KRF clear
Hardware
signal generation
generation by watch-
generation by the
instruction
instruction
dog timer overflow
KRn input
execution
execution
Watchdog flag (WDF)
0
1
Hold
0
Hold
Key return flag (KRF)
0
Hold
1
Hold
0
Figure 10-3. WDF Operation in Generating Each Signal
External RESET
WDF
Operation mode
Reset signal generation by
watchdog timer overflow
External RESET
signal generation
WDF clear
instruction
execution
Operation mode
HALT
mode
Operation
mode
HALT
mode
Operation
mode
HALT
mode
Operation mode
Internal reset operation
Internal reset operation
Internal reset operation
Reset signal generation by
watchdog timer overflow
*