HD6417034B RENESAS [Renesas Technology Corp], HD6417034B Datasheet - Page 372

• Manufacturer Part Number: HD6417034B
• Description: 32-Bit RISC Microcomputer
• Manufacturer: RENESAS [Renesas Technology Corp]

Section 12 Watchdog Timer (WDT)
12.3
12.3.1
To use the WDT as a watchdog timer, set the WT/IT and TME bits in TCSR to 1. Software must
prevent TCNT overflow by rewriting the TCNT value (normally by writing H'00) before overflow
occurs. If TCNT fails to be rewritten and overflows due to a system crash or the like, a WDTOVF
signal is output (figure 12.4). The WDTOVF signal can be used to reset external system devices.
The WDTOVF signal is output for 128 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
clock cycles.
When a watchdog reset is generated simultaneously with input at the RES pin, the software
distinguishes the RES reset from the watchdog reset by checking the WOVF bit in RSTCSR. The
RES reset takes priority. The WOVF bit is cleared to 0.
Rev. 7.00 Jan 31, 2006 page 346 of 658
REJ09B0272-0700
Operation
Operation in Watchdog Timer Mode