atmega32c1 ATMEL Corporation, atmega32c1 Datasheet - Page 82

• Manufacturer Part Number: atmega32c1
• Description: Atmega32m1 Automotive 8-bit Avr Microcontroller With 32k/64k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

10.2
10.2.1
82
External Interrupt Control Register A – EICRA
ATmega32/64/M1/C1
External Interrupt Mask Register – EIMSK
The External Interrupt Control Register A contains control bits for interrupt sense control.
• Bit 7..0 – ISC31, ISC30 - ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0
The External Interrupts 3 - 0 are activated by the external pins INT3:0 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 interrupt are defined in
nously. The value on the INT3:0 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 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 10-1.
Note:
• Bit 7..4 – Res: Reserved Bits
These bits are unused bits in the ATmega32/64/M1/C1, and will always read as zero.
• Bit 3..0 – INT3 - 0: External Interrupt Request 3:0 Enable
When an INT3 – INT0 bit is written to one and the I-bit in the Status Register (SREG) is set
(one), the corresponding external pin interrupt is enabled. The Interrupt Sense Control bits in the
External Interrupt Control Register A - EICRA defines whether the external interrupt is activated
on rising or falling edge or level sensed. Activity on any of these pins will trigger an interrupt
request even if the pin is enabled as an output. This provides a way of generating a software
interrupt.
Bit
Read/Write
Initial Value
Bit
Read/Write
Initial Value
ISCn1
0
0
1
1
1. n = 3, 2, 1 or 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.
ISCn0
ISC31
Interrupt Sense Control
R/W
7
0
R
7
–
0
0
1
0
1
ISC30
R/W
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.
6
0
R
6
–
0
ISC21
R/W
5
0
R
5
–
0
Table
(1)
ISC20
R/W
4
0
R
4
–
0
10-1. Edges on INT3..INT0 are registered asynchro-
ISC11
R/W
INT3
3
0
R
3
0
ISC10
R/W
INT2
2
0
R
2
0
ISC01
R/W
INT1
R/W
1
0
1
0
ISC00
R/W
INT0
R/W
0
0
0
0
EICRA
EIMSK
7647A–AVR–02/08