ATMEga64L ATMEL Corporation, ATMEga64L Datasheet - Page 89

• Manufacturer Part Number: ATMEga64L
• Description: 8-bit AVR Microcontroller with 64K Bytes In-System Programmable Flash
• Manufacturer: ATMEL Corporation

External Interrupt Control
Register B – EICRB
2490G–AVR–03/04
Table 48. Interrupt Sense Control
Note:
Table 49. Asynchronous External Interrupt Characteristics
• Bits 7..0 – ISC71, ISC70 - ISC41, ISC40: External Interrupt 7 - 4 Sense Control
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 50. 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 interrupt. 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 completion 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.
Table 50. Interrupt Sense Control
Note:
Bit
Read/Write
Initial Value
ISCn1
Symbol
ISCn1
Bits
t
0
0
1
1
0
0
1
1
INT
1. n = 3, 2, 1or 0.
1. n = 7, 6, 5 or 4.
ISCn0
ISCn0
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.
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.
Parameter
Minimum pulse width for
asynchronous External Interrupt
0
1
0
1
0
1
0
1
ISC71
R/W
7
0
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.
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.
ISC70
R/W
6
0
ISC61
R/W
5
0
(1)
(1)
ISC60
R/W
4
0
ISC51
R/W
Condition
3
0
ISC50
R/W
2
0
Min
ATmega64(L)
ISC41
R/W
1
0
Typ
50
ISC40
R/W
0
0
Max
EICRB
Units
ns
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