41594B datasheet(79/372 Pages) MICROCHIP

79 / 372 page

 2011-2012 Microchip Technology Inc.

Preliminary

DS41594B-page 79

PIC12LF1840T48A

8.1

Operation

Interrupts are disabled upon any device Reset. They

are enabled by setting the following bits:

• GIE bit of the INTCON register

• Interrupt Enable bit(s) for the specific interrupt

event(s)

• PEIE bit of the INTCON register (if the Interrupt

Enable bit of the interrupt event is contained in the

PIEx register)

The INTCON, PIR1 and PIR2 registers record individual

interrupts via interrupt flag bits. Interrupt flag bits will be

set, regardless of the status of the GIE, PEIE and

individual interrupt enable bits.

The following events happen when an interrupt event

occurs while the GIE bit is set:

• Current prefetched instruction is flushed

• GIE bit is cleared

• Current Program Counter (PC) is pushed onto the

stack

• Critical registers are automatically saved to the

shadow registers (See Section 8.5 “Automatic

Context Saving”)

• PC is loaded with the interrupt vector 0004h

The firmware within the Interrupt Service Routine (ISR)

should determine the source of the interrupt by polling

the interrupt flag bits. The interrupt flag bits must be

cleared before exiting the ISR to avoid repeated

interrupts. Because the GIE bit is cleared, any interrupt

that occurs while executing the ISR will be recorded

through its interrupt flag, but will not cause the

processor to redirect to the interrupt vector.

The RETFIE instruction exits the ISR by popping the

previous address from the stack, restoring the saved

context from the shadow registers and setting the GIE

bit.

For additional information on a specific interrupt’s

operation, refer to its peripheral chapter.

8.2

Interrupt Latency

Interrupt latency is defined as the time from when the

interrupt event occurs to the time code execution at the

interrupt vector begins. The latency for synchronous

interrupts is 3 or 4 instruction cycles. For asynchronous

interrupts, the latency is 3 to 5 instruction cycles,

depending on when the interrupt occurs. See Figure 8-3

and Figure 8-4 for more details.

Note 1: Individual interrupt flag bits are set,

regardless of the state of any other

enable bits.

2: All interrupts will be ignored while the GIE

bit is cleared. Any interrupt occurring

while the GIE bit is clear will be serviced

when the GIE bit is set again.

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