SH7046 Datasheet, PDF (353/611 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7046 Series

Section 11 Watchdog Timer
11.4 Operation
11.4.1 Watchdog Timer Mode
To use the WDT as a watchdog timer, set the WT/IT and TME bits of TCSR to 1. Software must
prevent TCNT overflow by rewriting the TCNT value (normally by writing H'00) before overflow
occurs. No TCNT overflows will occur while the system is operating normally, but if TCNT fails
to be rewritten and overflows occur due to a system crash or the like, a WDTOVF signal is output
externally. The WDTOVF signal can be used to reset the system. The WDTOVF signal is output
for 128 φ clock cycles.
If the RSTE bit in RSTCSR is set to 1, a signal to reset the chip will be generated internally
simultaneous to the WDTOVF signal when TCNT overflows. Either a power-on reset or a manual
reset can be selected by the RSTS bit in RSTCSR. The internal reset signal is output for 512 φ
clock cycles.
When a WDT overflow reset is generated simultaneously with a reset input at the RES pin, the
RES reset takes priority, and the WOVF bit in RSTCSR is cleared to 0.
The following are not initialized by a WDT reset signal:
• POE (port output enable) of MTU and MMT registers
• PFC (pin function controller) registers
• I/O port registers
These registers are initialized only by an external power-on reset.
Rev. 4.00 Dec 05, 2005 page 309 of 564
REJ09B0270-0400