PIC16F753 datasheet(159/230 Pages) MICROCHIP

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DS40001709C-page 159

PIC16F753/HV753

19.4

Interrupts

The PIC16F753/HV753 has multiple sources of

interrupt:

• External Interrupt (INT pin)

• Interrupt-On-Change (IOC) Interrupts

• Timer0 Overflow Interrupt

• Timer1 Overflow Interrupt

• Timer2 Match Interrupt

• Hardware Limit Timer (HLT) Interrupt

• Comparator Interrupt (C1/C2)

• ADC Interrupt

• Complementary Output Generator (COG)

• CCP1 Interrupt

• Flash Memory Self Write

The Interrupt Control register (INTCON) and Peripheral

Interrupt Request Registers (PIRx) record individual

interrupt requests in flag bits. The INTCON register

also has individual and global interrupt enable bits.

The Global Interrupt Enable bit, GIE of the INTCON

disables (if cleared) all interrupts. Individual interrupts

can be disabled through their corresponding enable

bits in the INTCON register and PIEx registers. GIE is

cleared on Reset.

When an interrupt is serviced, the following actions

occur automatically:

• The GIE is cleared to disable any further interrupt.

• The return address is pushed onto the stack.

• The PC is loaded with 0004h.

The Return from Interrupt instruction, RETFIE, exits

the interrupt routine, as well as sets the GIE bit, which

re-enables unmasked interrupts.

The following interrupt flags are contained in the

INTCON register:

• INT Pin Interrupt

• Interrupt-On-Change (IOC) Interrupts

• Timer0 Overflow Interrupt

The peripheral interrupt flags are contained in the PIR1

and PIR2 registers. The corresponding interrupt enable

bit is contained in the PIE1 and PIE2 registers.

The following interrupt flags are contained in the PIR1

• A/D Interrupt

• Comparator Interrupt

• Timer1 Overflow Interrupt

• Timer2 Match Interrupt

• Enhanced CCP Interrupt

For external interrupt events, such as the INT pin or

PORTA change interrupt, the interrupt latency will be

three or four instruction cycles. The exact latency

depends upon when the interrupt event occurs (see

Figure 19-8). The latency is the same for one or two-

cycle instructions. Once in the Interrupt Service

Routine, the source(s) of the interrupt can be

determined by polling the interrupt flag bits. The

interrupt flag bit(s) must be cleared in software before

re-enabling interrupts to avoid multiple interrupt

requests.

For

additional

information

Timer1,

Timer2,

comparators, ADC, Enhanced CCP modules, refer to

the respective peripheral section.

19.4.1

RA2/INT INTERRUPT

The external interrupt on the RA2/INT pin is edge-

triggered; either on the rising edge if the INTEDG bit of

the OPTION register is set, or the falling edge, if the

INTEDG bit is clear. When a valid edge appears on the

RA2/INT pin, the INTF bit of the INTCON register is set.

This interrupt can be disabled by clearing the INTE

control bit of the INTCON register. The INTF bit must

be cleared by software in the Interrupt Service Routine

before re-enabling this interrupt. The RA2/INT interrupt

can wake-up the processor from Sleep, if the INTE bit

was set prior to going into Sleep. See Section 19.7

“Power-Down Mode (Sleep)” for details on Sleep and

Figure 19-10 for timing of wake-up from Sleep through

RA2/INT interrupt.

Note 1: Individual interrupt flag bits are set,

regardless

the

status

their

corresponding mask bit or the GIE bit.

2: When an instruction that clears the GIE

bit is executed, any interrupts that were

pending for execution in the next cycle

are ignored. The interrupts, which were

ignored, are still pending to be serviced

when the GIE bit is set again.

Note:

The ANSEL register must be initialized to

configure an analog channel as a digital

input. Pins configured as analog inputs

will read ‘0’ and cannot generate an

interrupt.

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