581
15.5.2
Changing Value of PSS and CKS2 to CKS0
If bits PSS and CKS2 to CKS0 in TCSR are written to while the WDT is operating, errors could
occur in the incrementation. Software must stop the watchdog timer (by clearing the TME bit to 0)
before changing the value of bits PSS and CKS2 to CKS0.
15.5.3
Switching between Watchdog Timer Mode and Interval Timer Mode
If the mode is switched from watchdog timer to interval timer, or vice versa, while the WDT is
operating, errors could occur in the incrementation. Software must stop the watchdog timer (by
clearing the TME bit to 0) before switching the mode.
15.5.4
System Reset by
WDTOVF
Signal
If the
WDTOVF
output signal is input to the
RES
pin of the H8S/2633 Series, the H8S/2633
Series will not be initialized correctly. Make sure that the
WDTOVF
signal is not input logically
to the
RES
pin. To reset the entire system by means of the
WDTOVF
signal, use the circuit shown
in figure 15-9.
Reset input
Reset signal to entire system
H8S/2633 Series
RES
WDTOVF
Figure 15-9 Circuit for System Reset by
WDTOVF
Signal (Example)
15.5.5
Internal Reset in Watchdog Timer Mode
The H8S/2633 Series is not reset internally if TCNT overflows while the RSTE bit is cleared to 0
during watchdog timer operation, but TCNT and TCSR of the WDT are reset.
TCNT, TCSR, and RSTCSR cannot be written to while the
WDTOVF
signal is low. Also note
that a read of the WOVF flag is not recognized during this period. To clear the WOVF falg,
therefore, read TCSR after the
WDTOVF
signal goes high, then write 0 to the WOVF flag.