HD6412240 RENESAS [Renesas Technology Corp], HD6412240 Datasheet - Page 444

• Manufacturer Part Number: HD6412240
• Description: Renesas 16-Bit Single-Chip Microcomputer H8S Family / H8S/2200 Series
• Manufacturer: RENESAS [Renesas Technology Corp]

Section 11 Watchdog Timer
11.5.3
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.
11.5.4
If the WDTOVF output signal is input to the RES pin of the H8S/2245 Group, the H8S/2245
Group 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 11.9.
11.5.5
The H8S/2245 Group is not reset internally if TCNT overflows while the RSTE bit is cleared to 0
during watchdog timer operation, but TCNT and TSCR of the WDT are reset.
TCNT, TCSR, and RSTCR 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 flag, therefore,
read TCSR after the WDTOVF signal goes high, then write 0 to the WOVF flag.
11.5.6
When the OVF flag setting conflicts with the OVF flag reading in interval timer mode, writing 0
to the OVF bit may not clear the flag even though the OVF bit has been read while it is 1. If there
is a possibility that the OVF flag setting and reading will conflict, such as when the OVF flag is
polled with the interval timer interrupt disabled, read the OVF bit while it is 1 at least twice before
writing 0 to the OVF bit to clear the flag.
Rev.3.00 Mar. 26, 2007 Page 402 of 772
REJ09B0355-0300
Switching between Watchdog Timer Mode and Interval Timer Mode
System Reset by WDTOVF
Internal Reset in Watchdog Timer Mode
OVF Flag Clearing in Interval Timer Mode
Reset signal to entire system
Figure 11.9 Circuit for System Reset by WDTOVF
Reset input
WDTOVF
WDTOVF Signal
WDTOVF
WDTOVF
WDTOVF Signal (Example)
WDTOVF
WDTOVF
RES
H8S/2245