AT32UC3C2512C Automotive Atmel Corporation, AT32UC3C2512C Automotive Datasheet - Page 13

• Manufacturer Part Number: AT32UC3C2512C Automotive
• Manufacturer: Atmel Corporation

7701E–AVR–02/11
When an interrupt occurs, the global interrupt enable I-bit is cleared and all interrupts are dis-
abled. The user software can write a logical one to the I-bit to enable nested interrupts. All
enabled interrupts can then interrupt the current interrupt routine. The I-bit is automatically set
when a return from interrupt instruction, RETI, is executed.
There are basically two types of interrupts. The first type is triggered by an event that sets the
interrupt flag. For these interrupts, the program counter is vectored to the actual interrupt vec-
tor in order to execute the interrupt handling routine, and hardware clears the corresponding
interrupt flag. Interrupt flags can also be cleared by writing a logic one to the flag bit position(s)
to be cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is
cleared, the interrupt flag will be set and remembered until the interrupt is enabled or the flag
is cleared by software. Similarly, if one or more interrupt conditions occur while the global inter-
rupt enable bit is cleared, the corresponding interrupt flag(s) will be set and remembered until
the global interrupt enable bit is set, and will then be executed by order of priority.
The second type of interrupt will trigger as long as the interrupt condition is present. These
interrupts do not necessarily have interrupt flags. If the interrupt condition disappears before
the interrupt is enabled, the interrupt will not be triggered.
When the Atmel® AVR® exits from an interrupt, it will always return to the main program and
execute one more instruction before any pending interrupt is served.
Note that the status register is not automatically stored when entering an interrupt routine, nor
restored when returning from an interrupt routine. This must be handled by software.
When using the CLI instruction to disable interrupts, the interrupts will be immediately dis-
abled. No interrupt will be executed after the CLI instruction, even if it occurs simultaneously
with the CLI instruction. The following example shows how this can be used to avoid interrupts
during the timed EEPROM write sequence.
Assembly Code Example
C Code Example
in r16, SREG
cli
sbi EECR, EEMPE
sbi EECR, EEPE
out SREG, r16
char cSREG;
cSREG = SREG; /* store SREG value */
/* disable interrupts during timed sequence */
_CLI();
EECR |= (1<<EEMPE); /* start EEPROM write */
EECR |= (1<<EEPE);
SREG = cSREG; /* restore SREG value (I-bit) */
; disable interrupts during timed sequence
; store SREG value
; start EEPROM write
; restore SREG value (I-bit)
Atmel ATtiny24/44/84 [Preliminary]
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