AT89LP4052 datasheet(18/94 Pages) ATMEL

18 / 94 page

3547J–MICRO–10/09

AT89LP2052/LP4052

If a request is active and conditions are met for it to be acknowledged, a hardware subroutine

call to the requested service routine will be the next instruction executed. The call itself takes

four cycles. Thus, a minimum of five complete clock cycles elapsed between activation of an

interrupt request and the beginning of execution of the first instruction of the service routine.

A longer response time results if the request is blocked by one of the previously listed condi-

tions. If an interrupt of equal or higher priority level is already in progress, the additional wait time

depends on the nature of the other interrupt's service routine. If the instruction in progress is not

in its final clock cycle, the additional wait time cannot be more than 3 cycles, since the longest

are only 4 cycles long. If the instruction in progress is RETI or an access to IE or IP, the addi-

tional wait time cannot be more than 7 cycles (a maximum of three more cycles to complete the

instruction in progress, plus a maximum of 4 cycles to complete the next instruction). Thus, in a

single-interrupt system, the response time is always more than 5 clock cycles and less than

13 clock cycles. See Figures 14-1 and 14-2.

Figure 14-1. Minimum Interrupt Response Time

Figure 14-2. Maximum Interrupt Response Time

Clock Cycles

INT0

IE0

Instruction

LCALL

1st ISR Instr.

Cur. Instr.

Ack.

Clock Cycles

INT0

IE0

113

Instruction

RETI

4 Cyc. Instr.

LCALL

1st ISR In

Ack.

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