Datasheet

87
7766E–AVR–04/10
ATmega16U4/ATmega32U4
• Bit 3..0 – Res: Reserved Bits
These bits are reserved bits in the ATmega16U4/ATmega32U4 and always read as zero.
11.0.3 External Interrupt Mask Register – EIMSK
• Bits 7..0 – INT6, INT3 – INT0: External Interrupt Request 6, 3 - 0 Enable
When an INT[6;3:0] 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 Exter-
nal Interrupt Control Registers – EICRA and EICRB – 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.
11.0.4 External Interrupt Flag Register – EIFR
• Bits 7..0 – INTF6, INTF3 - INTF0: External Interrupt Flags 6, 3 - 0
When an edge or logic change on the INT[6;3:0] pin triggers an interrupt request, INTF7:0
becomes set (one). If the I-bit in SREG and the corresponding interrupt enable bit, INT[6;3:0] 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 INT[6;3:0] are configured as level interrupt. Note that when
entering sleep mode with the INT3:0 interrupts disabled, the input buffers on these pins will be
disabled. This may cause a logic change in internal signals which will set the INTF3:0 flags. See
“Digital Input Enable and Sleep Modes” on page 69 for more information.
11.0.5 Pin Change Interrupt Control Register - PCICR
• 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 Interrupt
Vector. PCINT7..0 pins are enabled individually by the PCMSK0 Register.
11.0.6 Pin Change Interrupt Flag Register – PCIFR
Bit 76543210
- INT6 - - INT3 INT2 INT1 IINT0 EIMSK
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
- INTF6 - - INTF3 INTF2 INTF1 IINTF0 EIFR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
– – – – –PCIE0PCICR
Read/WriteRRRRRRRR/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
– – – – –PCIF0PCIFR
Read/WriteRRRRRRRR/W
Initial Value 0 0 0 0 0 0 0 0