H8S2245 datasheet(438/818 Pages) RENESAS

438 / 818 page

Section 11 Watchdog Timer

Rev.3.00 Mar. 26, 2007 Page 396 of 772

REJ09B0355-0300

11.3

Operation

11.3.1

Watchdog Timer Operation

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.

H8S2245 Datasheet(PDF) 438 Page - Renesas Technology Corp