ATmega48/88/168
11.1.2
External Interrupt Mask Register – EIMSK
Bit
7
–
6
–
5
–
4
–
3
–
2
–
1
0
INT1
R/W
0
INT0
R/W
0
EIMSK
Read/Write
Initial Value
R
0
R
0
R
0
R
0
R
0
R
0
• Bit 7..2 – Res: Reserved Bits
These bits are unused bits in the ATmega48/88/168, and will always read as zero.
• Bit 1 – INT1: External Interrupt Request 1 Enable
When the INT1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the exter-
nal pin interrupt is enabled. The Interrupt Sense Control1 bits 1/0 (ISC11 and ISC10) in the
External Interrupt Control Register A (EICRA) define whether the external interrupt is activated
on rising and/or falling edge of the INT1 pin or level sensed. Activity on the pin will cause an
interrupt request even if INT1 is configured as an output. The corresponding interrupt of External
Interrupt Request 1 is executed from the INT1 Interrupt Vector.
• Bit 0 – INT0: External Interrupt Request 0 Enable
When the INT0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the exter-
nal pin interrupt is enabled. The Interrupt Sense Control0 bits 1/0 (ISC01 and ISC00) in the
External Interrupt Control Register A (EICRA) define whether the external interrupt is activated
on rising and/or falling edge of the INT0 pin or level sensed. Activity on the pin will cause an
interrupt request even if INT0 is configured as an output. The corresponding interrupt of External
Interrupt Request 0 is executed from the INT0 Interrupt Vector.
11.1.3
External Interrupt Flag Register – EIFR
Bit
7
6
–
5
–
4
–
3
–
2
–
1
INTF1
R/W
0
0
INTF0
R/W
0
–
R
0
EIFR
Read/Write
Initial Value
R
0
R
0
R
0
R
0
R
0
• Bit 7..2 – Res: Reserved Bits
These bits are unused bits in the ATmega48/88/168, and will always read as zero.
• Bit 1 – INTF1: External Interrupt Flag 1
When an edge or logic change on the INT1 pin triggers an interrupt request, INTF1 becomes set
(one). If the I-bit in SREG and the INT1 bit in EIMSK are set (one), the MCU will jump to the cor-
responding Interrupt Vector. The flag is cleared when the interrupt routine is executed.
Alternatively, the flag can be cleared by writing a logical one to it. This flag is always cleared
when INT1 is configured as a level interrupt.
• Bit 0 – INTF0: External Interrupt Flag 0
When an edge or logic change on the INT0 pin triggers an interrupt request, INTF0 becomes set
(one). If the I-bit in SREG and the INT0 bit in EIMSK are set (one), the MCU will jump to the cor-
responding Interrupt Vector. The flag is cleared when the interrupt routine is executed.
Alternatively, the flag can be cleared by writing a logical one to it. This flag is always cleared
when INT0 is configured as a level interrupt.
85
2545E–AVR–02/05
MICROCHIP [ MICROCHIP ]
