ATMEGA2561V ATMEL [ATMEL Corporation], ATMEGA2561V Datasheet - Page 18

• Manufacturer Part Number: ATMEGA2561V
• Description: 8-bit Microcontroller with 64K/128K/256K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Interrupt Response Time
18
ATmega640/1280/1281/2560/2561
neously with the CLI instruction. The following example shows how this can be used to
avoid interrupts during the timed EEPROM write sequence.
When using the SEI instruction to enable interrupts, the instruction following SEI will be
executed before any pending interrupts, as shown in this example.
The interrupt execution response for all the enabled AVR interrupts is five clock cycles
minimum. After five clock cycles the program vector address for the actual interrupt han-
dling routine is executed. During these five clock cycle period, the Program Counter is
pushed onto the Stack. The vector is normally a jump to the interrupt routine, and this
jump takes three clock cycles. If an interrupt occurs during execution of a multi-cycle
instruction, this instruction is completed before the interrupt is served. If an interrupt
occurs when the MCU is in sleep mode, the interrupt execution response time is
increased by five clock cycles. This increase comes in addition to the start-up time from
the selected sleep mode.
A return from an interrupt handling routine takes five clock cycles. During these five
clock cycles, the Program Counter (three bytes) is popped back from the Stack, the
Stack Pointer is incremented by three, and the I-bit in SREG is set.
Assembly Code Example
C Code Example
Assembly Code Example
C Code Example
in r16, SREG
cli
sbi EECR, EEMPE
sbi EECR, EEPE
out SREG, r16
char cSREG;
cSREG = SREG;
/* disable interrupts during timed sequence */
__disable_interrupt();
EECR |= (1<<EEMPE); /* start EEPROM write */
EECR |= (1<<EEPE);
SREG = cSREG; /* restore SREG value (I-bit) */
sei
sleep ; enter sleep, waiting for interrupt
; note: will enter sleep before any pending
; interrupt(s)
__enable_interrupt(); /* set Global Interrupt Enable */
__sleep(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */
; set Global Interrupt Enable
; disable interrupts during timed sequence
/* store SREG value */
; store SREG value
; start EEPROM write
; restore SREG value (I-bit)
2549K–AVR–01/07