4571 datasheet(22/126 Pages) RENESAS

22 / 126 page

Rev.1.02

May 25, 2007

Page 22 of 124

REJ03B0179-0102

4571 Group

(1) External 0 interrupt request flag (EXF0)

External 0 interrupt request flag (EXF0) is set to “1” when a

valid waveform is input to P20/INT0 pin.

The valid waveforms causing the interrupt must be retained at

their level for 4 clock cycles or more of the system clock (Refer

to Figure 22).

The state of EXF0 flag can be examined with the skip instruction

(SNZ0). Use the interrupt control register V1 to select the

interrupt or the skip instruction. The EXF0 flag is cleared to “0”

when an interrupt occurs or when the next instruction is skipped

with the skip instruction.

• External 0 interrupt activated condition

External 0 interrupt activated condition is satisfied when a

valid waveform is input to P20/INT0 pin.

The valid waveform can be selected from rising waveform,

falling waveform or both rising and falling waveforms. An

example of how to use the external 0 interrupt is as follows.

(1) Set the bit 3 of register I1 to “1” for the INT0 pin to be in the

input enabled state.

(2) Select the valid waveform with the bits 1 and 2 of register

I1.

(3) Clear the EXF0 flag to “0” with the SNZ0 instruction.

(4) Set the NOP instruction for the case when a skip is

performed with the SNZ0 instruction.

(5) Set both the external 0 interrupt enable bit (V10) and the

INTE flag to “1.”

The external 0 interrupt is now enabled. Now when a valid

waveform is input to the P20/INT0 pin, the EXF0 flag is set to

“1” and the external 0 interrupt occurs.

(2) External 1 interrupt request flag (EXF1)

External 1 interrupt request flag (EXF1) is set to “1” when a

valid waveform is input to P21/INT1 pin.

The valid waveforms causing the interrupt must be retained at

their level for 4 clock cycles or more of the system clock (Refer

to Figure 22).

The state of EXF1 flag can be examined with the skip instruction

(SNZ1). Use the interrupt control register V1 to select the

interrupt or the skip instruction. The EXF1 flag is cleared to “0”

when an interrupt occurs or when the next instruction is skipped

with the skip instruction.

• External 1 interrupt activated condition

External 1 interrupt activated condition is satisfied when a

valid waveform is input to P21/INT1 pin.

The valid waveform can be selected from rising waveform,

falling waveform or both rising and falling waveforms. An

example of how to use the external 1 interrupt is as follows.

(1) Set the bit 3 of register I2 to “1” for the INT1 pin to be in the

input enabled state.

(2) Select the valid waveform with the bits 1 and 2 of register

I2.

(3) Clear the EXF1 flag to “0” with the SNZ1 instruction.

(4) Set the NOP instruction for the case when a skip is

performed with the SNZ1 instruction.

(5) Set both the external 1 interrupt enable bit (V11) and the

INTE flag to “1.”

The external 1 interrupt is now enabled. Now when a valid

waveform is input to the P21/INT1 pin, the EXF1 flag is set to

“1” and the external 1 interrupt occurs.

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