84
7647H–AVR–03/12
Atmel ATmega16/32/64/M1/C1
10.2.2 External Interrupt Flag Register – EIFR
• Bit 7..4 – Res: Reserved Bits
These bits are unused bits in the ATmega16/32/64/M1/C1, and will always read as zero.
• Bit 3..0 – INTF3 - INTF0: External Interrupt Flag 3 - 0
When an edge or logic change on the INT3:0 pin triggers an interrupt request, INTF3:0 becomes
set (one). If the I-bit in SREG and the corresponding interrupt enable bit INT3:0 in EIMSK, are
set (one), the MCU will jump to the 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. These flags are
always cleared when INT3:0 are configured as a level interrupt.
10.2.3 Pin Change Interrupt Control Register - PCICR
• Bit 7..4 - Res: Reserved Bits
These bits are unused bits in the ATmega16/32/64/M1/C1, and will always read as zero.
• Bit 3 - PCIE3: Pin Change Interrupt Enable 3
When the PCIE3 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin
change interrupt 3 is enabled. Any change on any enabled PCINT26..24 pin will cause an inter-
rupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI3
Interrupt Vector. PCINT26..24 pins are enabled individually by the PCMSK3 Register.
• Bit 2 - PCIE2: Pin Change Interrupt Enable 2
When the PCIE2 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin
change interrupt 2 is enabled. Any change on any enabled PCINT23..16 pin will cause an inter-
rupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI2
Interrupt Vector. PCINT23..16 pins are enabled individually by the PCMSK2 Register.
• Bit 1 - PCIE1: Pin Change Interrupt Enable 1
When the PCIE1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin
change interrupt 1 is enabled. Any change on any enabled PCINT15..8 pin will cause an inter-
rupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI1
Interrupt Vector. PCINT15..8 pins are enabled individually by the PCMSK1 Register.
• Bit 0 - PCIE0: Pin Change Interrupt Enable 0
When the PCIE0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin
change interrupt 0 is enabled. Any change on any enabled PCINT7..0 pin will cause an interrupt.
The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI0 Inter-
rupt Vector. PCINT7..0 pins are enabled individually by the PCMSK0 Register.
Bit 76543210
– – – – INTF3 INTF2 INTF1 INTF0 EIFR
Read/Write R R R R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
– – – – PCIE3 PCIE2 PCIE1 PCIE0 PCICR
Read/Write R R R R R R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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