ATtiny25 datasheet(13/196 Pages) ATMEL

13 / 196 page

7598H–AVR–07/09

ATtiny25/45/85

When using the SEI instruction to enable interrupts, the instruction following SEI will be exe-

cuted before any pending interrupts, as shown in this example.

4.8.1

Interrupt Response Time

The interrupt execution response for all the enabled AVR interrupts is four clock cycles mini-

mum. After four clock cycles the Program Vector address for the actual interrupt handling routine

is executed. During this four 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 four 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 four clock cycles. During these four clock

cycles, the Program Counter (two bytes) is popped back from the Stack, the Stack Pointer is

incremented by two, and the I-bit in SREG is set.

AVR ATtiny25/45/85 Memories

This section describes the different memories in the ATtiny25/45/85. The AVR architecture has

two main memory spaces, the Data memory and the Program memory space. In addition, the

ATtiny25/45/85 features an EEPROM Memory for data storage. All three memory spaces are lin-

ear and regular.

5.1

In-System Re-programmable Flash Program Memory

The ATtiny25/45/85 contains 2/4/8K byte On-chip In-System Reprogrammable Flash memory

for program storage. Since all AVR instructions are 16 or 32 bits wide, the Flash is organized as

1024/2048/4096 x 16.

The Flash memory has an endurance of at least 10,000 write/erase cycles. The ATtiny25/45/85

Program Counter (PC) is 10/11/12 bits wide, thus addressing the 1024/2048/4096 Program

memory locations. “Memory Programming” on page 134 contains a detailed description on Flash

data serial downloading using the SPI pins.

Constant tables can be allocated within the entire Program memory address space (see the

LPM – Load Program memory instruction description).

Timing diagrams for instruction fetch and execution are presented in “Instruction Execution Tim-

ing” on page 11.

Assembly Code Example

sei

; set Global Interrupt Enable

sleep

; enter sleep, waiting for interrupt

; note: will enter sleep before any pending

; interrupt(s)

C Code Example

_SEI(); /* set Global Interrupt Enable */

_SLEEP(); /* enter sleep, waiting for interrupt */

/* note: will enter sleep before any pending interrupt(s) */

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