H8SLASH3028F datasheet(671/923 Pages) RENESAS

671 / 923 page

Rev. 2.00, 09/03, page 641 of 890

20.4

Software Standby Mode

20.4.1

Transition to Software Standby Mode

To enter software standby mode, execute the SLEEP instruction while the SSBY bit is set to 1 in

SYSCR.

In software standby mode, current dissipation is reduced to an extremely low level because the

CPU, clock, and on-chip supporting modules all halt. The DMAC and on-chip supporting modules

are reset and halted. As long as the specified voltage is supplied, however, CPU register contents

and on-chip RAM data are retained. The settings of the I/O ports and DRAM interface* are also

held. When the WDT is used as a watchdog timer (WT/

IT = 1), the TME bit must be cleared to 0

before setting SSBY. Also, when setting TME to 1, SSBY should be cleared to 0.

Clear the BRLE bit in BRCR (inhibiting bus release) before making a transition to software

standby mode.

Note: * RTCNT and bits 7 and 6 of RTMCSR are initialized. Other bits and registers hold their

previous states.

20.4.2

Exit from Software Standby Mode

Software standby mode can be exited by input of an external interrupt at the NMI,

IRQ

0, IRQ1, or

IRQ

2 pin, or by input at the RES or STBY pin.

Exit by Interrupt: When an NMI, IRQ0, IRQ1, or IRQ2 interrupt request signal is received, the

clock oscillator begins operating. After the oscillator settling time selected by bits STS2 to STS0

in SYSCR, stable clock signals are supplied to the entire chip, software standby mode ends, and

interrupt exception handling begins. Software standby mode is not exited if the interrupt enable

bits of interrupts IRQ0, IRQ1, and IRQ2 are cleared to 0, or if these interrupts are masked in the

CPU.

Exit by

RES

RES Input: When the RES input goes low, the clock oscillator starts and clock pulses are

supplied immediately to the entire chip. The

RES signal must be held low long enough for the

clock oscillator to stabilize. When

RES goes high, the CPU starts reset exception handling.

Exit by

STBY

STBY Input: Low input at the STBY pin causes a transition to hardware standby mode.

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