PIC16F1938-ESLASHP datasheet(73/418 Pages) MICROCHIP

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Preliminary

DS41364A-page 71

PIC16F193X/LF193X

4.1

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

PIE1, PIE2 and PIE3 registers)

The INTCON, PIR1, PIR2 and PIR3 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

• PC is loaded with the interrupt vector 0004h

The ISR determines 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.

4.2

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 4-3

for timing details.

FIGURE 4-3:

INT PIN INTERRUPT TIMING

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.

OSC1

CLKOUT

INT pin

INTF flag

(INTCON<1>)

GIE bit

(INTCON<7>)

INSTRUCTION FLOW

Instruction

Fetched

Instruction

Executed

Interrupt Latency

PC + 1

0004h

0005h

Inst (0004h)

Inst (0005h)

Dummy Cycle

Inst (PC)

Inst (PC + 1)

Inst (PC – 1)

Inst (0004h)

Dummy Cycle

Inst (PC)

—

Note 1:

INTF flag is sampled here (every Q1).

Asynchronous interrupt latency = 3-5 TCY. Synchronous latency = 3-4 TCY, where TCY = instruction cycle time.

Latency is the same whether Inst (PC) is a single cycle or a 2-cycle instruction.

CLKOUT is available only in INTOSC and RC Oscillator modes.

For minimum width of INT pulse, refer to AC specifications in Section 28.0 “Electrical Specifications”.

INTF is enabled to be set any time during the Q4-Q1 cycles.

(1)

(2)

(3)

(4)

(5)

(1)

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