Microchip Technology AC244045 Data Sheet

DS41440C-page 86

 2010-2012 Microchip Technology Inc.

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, PIR2, PIR3 and PIR4 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 

)

• 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.

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 three or four instruction cycles. For
asynchronous interrupts, the latency is three to five
instruction cycles, depending on when the interrupt
occurs. See 

 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.