ATmega64A datasheet(66/392 Pages) ATMEL

66 / 392 page

8160C–AVR–07/09

ATmega64A

Note:

1. n = 3, 2, 1or 0.

When changing the ISCn1/ISCn0 bits, the interrupt must be disabled by clearing its Interrupt

Enable bit in the EIMSK Register. Otherwise an interrupt can occur when the bits are changed.

12.1.2

EICRB – External Interrupt Control Register B

• Bits 7:0 – ISC71, ISC70 - ISC41, ISC40: External Interrupt 7 - 4 Sense Control Bits

The External Interrupts 7 - 4 are activated by the external pins INT7:4 if the SREG I-flag and the

corresponding interrupt mask in the EIMSK is set. The level and edges on the external pins that

activate the interrupts are defined in Table 12-3. The value on the INT7:4 pins are sampled

before detecting edges. If edge or toggle interrupt is selected, pulses that last longer than one

clock period will generate an interrupt. Shorter pulses are not guaranteed to generate an inter-

rupt. Observe that CPU clock frequency can be lower than the XTAL frequency if the XTAL

divider is enabled. If low level interrupt is selected, the low level must be held until the comple-

tion of the currently executing instruction to generate an interrupt. If enabled, a level triggered

interrupt will generate an interrupt request as long as the pin is held low.

Note:

1. n = 7, 6, 5 or 4.

When changing the ISCn1/ISCn0 bits, the interrupt must be disabled by clearing its Interrupt

Enable bit in the EIMSK Register. Otherwise an interrupt can occur when the bits are changed.

Table 12-1.

Interrupt Sense Control(1)

ISCn1

ISCn0

Description

The low level of INTn generates an interrupt request.

Reserved

The falling edge of INTn generates asynchronously an interrupt request.

The rising edge of INTn generates asynchronously an interrupt request.

Table 12-2.

Asynchronous External Interrupt Characteristics

Symbol

Parameter

Condition

Min

Typ

Max

Units

tINT

Minimum pulse width for asynchronous

External Interrupt

Bit

765

43210

0x3A (0x5A)

ISC71

ISC70

ISC61

ISC60

ISC51

ISC50

ISC41

ISC40

EICRB

Read/Write

R/W

Initial Value

000

00000

Table 12-3.

Interrupt Sense Control

(1)

ISCn1

ISCn0

Description

The low level of INTn generates an interrupt request.

Any logical change on INTn generates an interrupt request

The falling edge between two samples of INTn generates an interrupt request.

The rising edge between two samples of INTn generates an interrupt request.

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