SH7018 datasheet(211/431 Pages) RENESAS

211 / 431 page

195

Writing to the RSTCSR: The RSTCSR must be written by a word access to address

H'FFFF8612. It cannot be written by byte transfer instructions.

Procedures for writing 0 in WOVF (bit 7) and for writing to RSTE (bit 6) and RSTS (bit 5) are

different, as shown in figure 11.3.

To write 0 in the WOVF bit, the write data must be H'A5 in the upper byte and H'00 in the lower

byte. This clears the WOVF bit to 0. The RSTE and RSTS bits are not affected. To write to the

RSTE and RSTS bits, the upper byte must be H'5A and the lower byte must be the write data. The

values of bits 6 and 5 of the lower byte are transferred to the RSTE and RSTS bits, respectively.

The WOVF bit is not affected.

H'A5

H'FFFF8612

Address:

Writing 0 to the WOVF bit

H'00

H'5A

H'FFFF8612

Address:

Writing to the RSTE and RSTS bits

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

RSTE of RSTCSR is set to 1 and a problem such as system runaway occurs, the value of TCNT is

not overwritten and an overflow results. This causes WDT to generate an internal reset signal for

the chip. The internal reset signal is output for 512

φ clock cycles. Figure 11.4 shows the timing.

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:

SH7018 Datasheet(PDF) 211 Page - Renesas Technology Corp