
70
8155C–AVR–02/11
ATmega32A
low level interrupt is selected, the low level must be held until the completion of the currently
executing instruction to generate an interrupt.
Bit 1, 0 – ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0
The External Interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the corre-
sponding interrupt mask are set. The level and edges on the external INT0 pin that activate the
interrupt are defined in Table 13-2. The value on the INT0 pin is 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. If low level
interrupt is selected, the low level must be held until the completion of the currently executing
instruction to generate an interrupt.
13.1.2
MCUCSR – MCU Control and Status Register
Bit 6 – ISC2: Interrupt Sense Control 2
The Asynchronous External Interrupt 2 is activated by the external pin INT2 if the SREG I-bit and
the corresponding interrupt mask in GICR are set. If ISC2 is written to zero, a falling edge on
INT2 activates the interrupt. If ISC2 is written to one, a rising edge on INT2 activates the inter-
rupt. Edges on INT2 are registered asynchronously. Pulses on INT2 wider than the minimum
pulse width given in Table 13-3 will generate an interrupt. Shorter pulses are not guaranteed to
generate an interrupt. When changing the ISC2 bit, an interrupt can occur. Therefore, it is rec-
ommended to first disable INT2 by clearing its Interrupt Enable bit in the GICR Register. Then,
Table 13-1.
Interrupt 1 Sense Control
ISC11
ISC10
Description
0
The low level of INT1 generates an interrupt request.
0
1
Any logical change on INT1 generates an interrupt request.
1
0
The falling edge of INT1 generates an interrupt request.
1
The rising edge of INT1 generates an interrupt request.
Table 13-2.
Interrupt 0 Sense Control
ISC01
ISC00
Description
0
The low level of INT0 generates an interrupt request.
0
1
Any logical change on INT0 generates an interrupt request.
1
0
The falling edge of INT0 generates an interrupt request.
1
The rising edge of INT0 generates an interrupt request.
Bit
7
6543
210
JTD
ISC2
–
JTRF
WDRF
BORF
EXTRF
PORF
MCUCSR
Read/Write
R/W
R
R/W
Initial Value
0
See Bit Description