SH7713 datasheet(344/904 Pages) RENESAS

344 / 904 page

Section 10 Power-Down Modes

Rev.1.50 Aug. 30, 2006 Page 304 of 860

REJ09B0288-0150

The procedure for switching to software standby mode is as follows:

1. Clear the TME bit in the WDT’s timer control register (WTCSR) to 0 to stop the WDT.

2. Set the WDT’s timer counter (WTCNT) to 0 and the CKS2 to CKS0 bits in WTCSR to

appropriate values to secure the specified oscillation settling time.

3. After the STBY bit in STBCR is set to 1, a SLEEP instruction is executed.

4. Software standby mode is entered and the clocks within the chip are halted. The STATUS1

and STATUS0 pins output low and high, respectively.

Canceling Software Standby Mode: Software standby mode is canceled by an interrupt (NMI,

IRQ, IRL, or RTC) or a reset.

• Canceling with an Interrupt

The on-chip WDT can be used for hot starts. When the chip detects an NMI, IRQ*

1, IRL*1, or

RTC*

1 interrupt, the clock will be supplied to the entire chip and software 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 exception handling then begins and a code indicating the

interrupt source is set in INTEVT and INTEVT2. After the branch to the interrupt handling

routine, clear the STBY bit in STBCR. The WDT stops automatically. If the STBY bit is not

cleared, the WDT continues operation and a transition is made to software standby mode*

2 when

WTCNT reaches H'80. A manual reset is not accepted until the STBY bit is cleared to 0.

Interrupts are accepted in software standby mode even when the BL bit in SR is 1. If necessary,

save SPC and SSR to the stack before executing the SLEEP instruction.

Immediately after an interrupt is detected, the phase of the CKIO pin clock output may be

unstable, until the software standby mode is canceled.

Notes: 1. Only when the RTC is used, software standby mode can be canceled by an IRQ, IRL,

or RTC.

2. This standby mode can be canceled only by a power-on reset.

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