Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 76
defined in Table 13-1. Edges on INT2:INT0 are registered asynchronously. Pulses on INT2:0 pins wider than
the minimum pulse width given in ”External interrupts characteristics” on page 334 will generate an interrupt.
Shorter pulses are not guaranteed to generate an interrupt. 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. When changing the ISCn bit,
an interrupt can occur. Therefore, it is recommended to first disable INTn by clearing its Interrupt Enable bit in
the EIMSK Register. Then, the ISCn bit can be changed. Finally, the INTn interrupt flag should be cleared by
writing a logical one to its Interrupt Flag bit (INTFn) in the EIFR Register before the interrupt is re-enabled.
Note: 1. n = 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.
13.2.2 EIMSK – External Interrupt Mask Register
• Bits 2:0 – INT2:0: External Interrupt Request 2 - 0 Enable
When an INT2:0 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 External Interrupt Control Register,
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.
13.2.3 EIFR –External Interrupt Flag Register
• Bits 2:0 – INTF2:0: External Interrupt Flags 2 - 0
When an edge or logic change on the INT2:0 pin triggers an interrupt request, INTF2:0 becomes set (one). If the
I-bit in SREG and the corresponding interrupt enable bit, INT2:0 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 INT2:0 are configured as level
interrupt. Note that when entering sleep mode with the INT2:0 interrupts disabled, the input buffers on these
pins will be disabled. This may cause a logic change in internal signals which will set the INTF2:0 flags. See
”Digital Input Enable and Sleep Modes” on page 84 for more information.
Table 13-1. Interrupt Sense Control
(1)
ISCn1 ISCn0 Description
0 0 The low level of INTn generates an interrupt request
0 1 Any edge of INTn generates asynchronously an interrupt request
1 0 The falling edge of INTn generates asynchronously an interrupt request
1 1 The rising edge of INTn generates asynchronously an interrupt request
Bit 76543210
0x1D (0x3D)
– – – – – INT2 INT1 IINT0 EIMSK
Read/Write RRRRRR/WR/WR/W
Initial Value00000000
Bit 76543210
0x1C (0x3C)
– – – – – INTF2 INTF1 IINTF0 EIFR
Read/WriteR/WRRRRR/WR/WR/W
Initial Value00000000