PIC16F722AT-ISS Datasheet, PDF (38/286 Pages) Microchip Technology – 28-Pin Flash Microcontrollers with nanoWatt XLP Technology

PIC16(L)F722A/723A
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 and PIE2 registers)
The INTCON, PIR1 and PIR2 registers record individ-
ual 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 and setting the GIE bit.
For additional information on a specific interrupt’s
operation, refer to its peripheral chapter.
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.
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 instruction cycles. For asynchronous
interrupts, the latency is 3 to 4 instruction cycles,
depending on when the interrupt occurs. See Figure 4-2
for timing details.
FIGURE 4-2:
INT PIN INTERRUPT TIMING
OSC1
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
CLKOUT ⁽³⁾
(4)
INT pin
(1)
INTF flag
(INTCON<1>)
(1)
(5)
GIE bit
(INTCON<7>)
Interrupt Latency ⁽²⁾
INSTRUCTION FLOW
PC
PC
Instruction
Fetched
Inst (PC)
PC + 1
Inst (PC + 1)
PC + 1
—
0004h
Inst (0004h)
0005h
Inst (0005h)
Instruction
Executed
Inst (PC – 1)
Inst (PC)
Dummy Cycle
Dummy Cycle
Inst (0004h)
Note 1: INTF flag is sampled here (every Q1).
2: Asynchronous interrupt latency = 3-4 TCY. Synchronous latency = 3 TCY, where TCY = instruction cycle time. Latency
is the same whether Inst (PC) is a single cycle or a 2-cycle instruction.
3: CLKOUT is available only in INTOSC and RC Oscillator modes.
4: For minimum width of INT pulse, refer to AC specifications in Section 23.0 “Electrical Specifications”.
5: INTF is enabled to be set any time during the Q4-Q1 cycles.
DS41417B-page 38
 2010-2012 Microchip Technology Inc.