SH7014 datasheet(332/754 Pages) RENESAS

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11. Watchdog Timer (WDT)

Rev.5.00 Sep. 27, 2007 Page 298 of 716

REJ09B0398-0500

H'A5

H'FFFF8612

Address:

Writing 0 to the WOVF bit

H'00

H'5A

H'FFFF8612

Address:

Writing to the RSTE bit

Write data

Figure 11.3 Writing to the RSTCSR

Reading from the TCNT, TCSR, and RSTCSR: TCNT, TCSR, and RSTCSR are read like

other registers. Use byte transfer instructions. The read addresses are H'FFFF8610 for the TCSR,

H'FFFF8611 for the TCNT, and H'FFFF8613 for the RSTCSR.

11.3

Operation

11.3.1

Watchdog Timer Mode

To use the WDT as a watchdog timer, set the WT/

IT and TME bits of the 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 the

TCNT fails to be rewritten and overflows occur due to a system crash or the like, a

WDTOVF

signal is output externally (figure 11.4). 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 the RSTCSR is set to 1, a signal to reset the chip will be generated internally

simultaneous to the

WDTOVF signal when TCNT overflows. The internal reset signal is output

for 512

φ clock cycles.

When a watchdog overflow reset is generated simultaneously with a reset input at the

RES pin, the

RES reset takes priority, and the WOVF bit is cleared to 0.

The following are not initialized a WDT reset signal:

• PFC (Pin Function Controller) function register

• I/O port register

Initializing is only possible by external power-on reset.

SH7014 Datasheet(PDF) 332 Page - Renesas Technology Corp

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