M38K09RFS datasheet(230/328 Pages) RENESAS

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2.12 Standby function

Rev.2.00

Oct 05, 2006

page 101 of 111

38K0 Group

REJ09B0337-0200

APPLICATION

sRestoration by interrupt request

In the wait mode, the occurrence of an interrupt request releases the wait mode and supply of the

internal clock

φ to the CPU is started. At the same time, the interrupt request used for restoration

is accepted, so the interrupt processing routine is executed.

However, when using an interrupt request for restoration from the wait mode, in order to enable the

selected interrupt, you must execute the STP instruction after setting the following conditions.

[Necessary register setting]

➀ Interrupt disable flag I = “0” (interrupt enabled)

➁ Interrupt request bit of interrupt source to be used for restoration = “0” (no interrupt request issued)

➂ Interrupt enable bit of interrupt source to be used for restoration = “1” (interrupts enabled)

For more details concerning interrupts, refer to “2.2 Interrupts”.

2.12.5 Notes on stand-by function

In stand-by state*1 for low-power dissipation, do not make input levels of an input port and an I/O port

“undefined”.

Pull-up (connect the port to VCC) these ports through a resistor.

When determining a resistance value, note the following points:

• External circuit

• Variation of output levels during the ordinary operation

When using built-in pull-up resistor, note on varied current values.

• When setting as an input port: Fix its input level

• When setting as an output port: Prevent current from flowing out to external

q Reason

The potential which is input to the input buffer in a microcomputer is unstable in the state that input

levels of an input port and an I/O port are “undefined”. This may cause power source current.

*1 stand-by state :

the stop mode by executing the STP instruction

the wait mode by executing the WIT instruction

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