attiny11 ATMEL Corporation, attiny11 Datasheet - Page 31

• Manufacturer Part Number: attiny11
• Description: 8-bit Microcontroller With 1k Byte Flash
• Manufacturer: ATMEL Corporation

Interrupt Handling
Interrupt Response Time
External Interrupt
1006F–AVR–06/07
The ATtiny11/12 has two 8-bit Interrupt Mask control registers; GIMSK – General Inter-
rupt Mask register and TIMSK – Timer/Counter Interrupt Mask register.
When an interrupt occurs, the Global Interrupt Enable I-bit is cleared (zero) and all inter-
rupts are disabled. The user software can set (one) the I-bit to enable nested interrupts.
The I-bit is set (one) when a Return from Interrupt instruction – RETI – is executed.
When the Program Counter is vectored to the actual interrupt vector in order to execute
the interrupt handling routine, hardware clears the corresponding flag that generated the
interrupt. Some of the 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 when the corresponding interrupt enable bit is cleared
(zero), the interrupt flag will be set and remembered until the interrupt is enabled, or the
flag is cleared by software.
If one or more interrupt conditions occur when the global interrupt enable bit is cleared
(zero), the corresponding interrupt flag(s) will be set and remembered until the global
interrupt enable bit is set (one), and will be executed by order of priority.
Note that external level interrupt does not have a flag, and will only be remembered for
as long as the interrupt condition is active.
Note that the status register is not automatically stored when entering an interrupt rou-
tine and restored when returning from an interrupt routine. This must be handled by
software.
The interrupt execution response for all the enabled AVR interrupts is 4 clock cycles
minimum. After the 4 clock cycles, the program vector address for the actual interrupt
handling routine is executed. During this 4-clock-cycle period, the Program Counter (9
bits) is pushed onto the Stack. The vector is normally a relative jump to the interrupt rou-
tine, and this jump takes 2 clock cycles. If an interrupt occurs during execution of a
multi-cycle instruction, this instruction is completed before the interrupt is served. In
ATtiny12, if an interrupt occurs when the MCU is in Sleep mode, the interrupt response
time is increased by 4 clock cycles.
A return from an interrupt handling routine takes 4 clock cycles. During these 4 clock
cycles, the Program Counter (9 bits) is popped back from the Stack, and the I-flag in
SREG is set. When AVR exits from an interrupt, it will always return to the main program
and execute one more instruction before any pending interrupt is served.
The external interrupt is triggered by the INT0 pin. Observe that, if enabled, the interrupt
will trigger even if the INT0 pin is configured as an output. This feature provides a way of
generating a software interrupt. The external interrupt can be triggered by a falling or ris-
ing edge, a pin change, or a low level. This is set up as indicated in the specification for
the MCU Control Register – MCUCR. When the external interrupt is enabled and is con-
figured as level triggered, the interrupt will trigger as long as the pin is held low.
The external interrupt is set up as described in the specification for the MCU Control
Register – MCUCR.
$004
$005
;
$006
…
MAIN:
…
rjmp
rjmp
<instr>
…
xxx
EE_RDY
ANA_COMP
…
; EEPROM Ready handler
; Analog Comparator handler
; Main program start
ATtiny11/12
31