HD6412240 RENESAS [Renesas Technology Corp], HD6412240 Datasheet - Page 438

• 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
11.3
11.3.1
To use the WDT as a watchdog timer, set the WT/IT and TME bits to 1. Software must prevent
TCNT overflows by rewriting the TCNT value (normally be writing H'00) before overflows
occurs. This ensures that TCNT does not overflow while the system is operating normally. If
TCNT overflows without being rewritten because of a system crash or other error, the WDTOVF
signal is output. This is shown in figure 11.4. This WDTOVF signal can be used to reset the
system. The WDTOVF signal is output for 132 states when RSTE = 1, and for 130 states when
RSTE = 0.
If TCNT overflows when 1 is set in the RSTE bit in RSTCSR, a signal that resets the H8S/2245
Group internally is generated at the same time as the WDTOVF signal. This reset can be selected
as a power-on reset or a manual reset, depending on the setting of the RSTS bit in RSTCSR. The
internal reset signal is output for 518 states.
If a reset caused by a signal input to the RES pin occurs at the same time as a reset caused by a
WDT overflow, the RES pin reset has priority and the WOVF flag in RSTCSR is cleared to 0.
Rev.3.00 Mar. 26, 2007 Page 396 of 772
REJ09B0355-0300
Operation
Watchdog Timer Operation