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Renesas SH7641 User Manual

Page 223

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Section 6 Power-Down Modes

Rev. 4.00 Sep. 14, 2005 Page 173 of 982

REJ09B0023-0400

2. Canceling Standby Mode

Standby mode is canceled by interrupts (

NMI, IRQ) or a reset.

• Canceling with an Interrupt

The on-chip WDT can be used for hot starts. When an interrupt request is detected at the rising
or falling edge of

NMI or IRQ, the clock will be supplied to the entire chip and standby mode

canceled after the time set in the WDT's timer control/status register has elapsed. The
STATUS1 and STATUS0 pins go low. Interrupt handling then begins and a code indicating
the interrupt source is set in the INTEVT2 registers. After the branch to the interrupt handling
routine, clear the STBY bit in the STBCR register. WDT stops automatically. If the STBY bit
is not cleared, WDT continues operation and a transition is made to standby mode* when the
WTCNT reaches H'80. A manual reset will not be accepted while the STBY bit is set.
Interrupts are accepted in standby mode even when the BL bit in the SR register is 1. If
necessary, save SPC and SSR to the stack before executing the SLEEP instruction.

Immediately after an interrupt is detected and until the system is taken out of standby mode,
the phase of the clock outputs from the CKIO and CKIO2 pins may be unstable.

Notes: * This standby mode can be canceled only by a power-on reset.

WTCNT value

H'FF

H'80

Time

Interrupt
request

WDT overflow and branch to
interrupt handling routine

Crystal oscillator settling
time and PLL synchronization
time

Clear bit STBCR.STBY before
WTCNT reaches H'80. When
STBCR. STBY is cleared, WTCNT
halts automatically.

Figure 6.1 Canceling Standby Mode with STBCR.STBY

• Canceling with a Reset

Standby mode is canceled by a reset using the

RESETP or RESETM pin. Keep the RESETP or

RESETM pin low until the clock oscillation settles. The internal clock will continue to be
output to the CKIO pin.

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