HD6417618 datasheet(256/646 Pages) RENESAS

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Section 10 Power-Down Modes

Rev. 6.00 Jun. 12, 2007 Page 224 of 610

REJ09B0131-0600

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

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

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

appropriate values to secure the specified oscillation settling time.

3. After setting the STBY bit in STBCR to 1, execute the SLEEP instruction.

4. Software standby mode is entered and the clocks within this LSI are halted.

10.5.2

Canceling Software Standby Mode

Software standby mode is canceled by interrupts (NMI, IRQ) or a reset.

Canceling with Interrupt: The WDT can be used for hot starts. When an NMI or IRQ interrupt is

detected, the clock will be supplied to the entire LSI and software standby mode will be canceled

after the time set in the timer control/status register of the WDT has elapsed. Interrupt exception

handling is then executed. After the branch to the interrupt handling routine, clear the STBY bit in

STBCR. WTCNT stops automatically. If the STBY bit is not cleared, WTCNT continues

operation and a transition is made to software standby mode* when it reaches H'80. This function

prevents data destruction due to the voltage rise by an unstable power supply voltage.

IRQ cancels the software standby mode when the input condition matches the specified detect

condition while the IRQn1S and IRQn0S bits in IRQCR are not B'00 (settings other than the low

level detection). When the priority level of an IRQ interrupt is lower than the interrupt mask level

set in the status register (SR) of the CPU, the execution of the instruction following the SLEEP

instruction starts again after the cancellation of software standby mode. When the priority level of

an IRQ interrupt is higher than the interrupt mask level set in the status register (SR) of the CPU,

IRQ interrupt exception handling is executed after the cancellation of software standby mode.

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

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