Datasheet

PIC16F913/914/916/917/946
DS41250F-page 230 © 2007 Microchip Technology Inc.
16.3 Interrupts
The PIC16F91X/946 has multiple sources of interrupt:
• External Interrupt RB0/INT/SEG0
• TMR0 Overflow Interrupt
• PORTB Change Interrupts
• 2 Comparator Interrupts
• A/D Interrupt
• Timer1 Overflow Interrupt
• EEPROM Data Write Interrupt
• Fail-Safe Clock Monitor Interrupt
• LCD Interrupt
• PLVD Interrupt
• USART Receive and Transmit interrupts
• CCP1 and CCP2 Interrupts
• Timer2 Interrupt
The Interrupt Control (INTCON), Peripheral Interrupt
Request 1 (PIR1) and Peripheral Interrupt Request 2
(PIR2) registers record individual interrupt requests in
flag bits. The INTCON register also has individual and
global interrupt enable bits.
A Global Interrupt Enable bit, GIE of the INTCON
register, enables (if set) all unmasked interrupts, or
disables (if cleared) all interrupts. Individual interrupts
can be disabled through their corresponding enable
bits in the INTCON, PIE1 and PIE2 registers. GIE is
cleared on Reset.
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
• PORTB Change Interrupt
• TMR0 Overflow Interrupt
The peripheral interrupt flags are contained in the special
registers, PIR1 and PIR2. The corresponding interrupt
enable bit are contained in the special registers, PIE1
and PIE2.
The following interrupt flags are contained in the PIR1
register:
• EEPROM Data Write Interrupt
• A/D Interrupt
• USART Receive and Transmit Interrupts
• Timer1 Overflow Interrupt
• CCP1 Interrupt
• SSP Interrupt
• Timer2 Interrupt
The following interrupt flags are contained in the PIR2
register:
• Fail-Safe Clock Monitor Interrupt
• Comparator 1 and 2 Interrupts
• LCD Interrupt
• PLVD Interrupt
• CCP2 Interrupt
When an interrupt is serviced:
• The GIE is cleared to disable any further interrupt.
• The return address is pushed onto the stack.
• The PC is loaded with 0004h.
For external interrupt events, such as the INT pin or
PORTB change interrupt, the interrupt latency will be
three or four instruction cycles. The exact latency
depends upon when the interrupt event occurs (see
Figure 16-8). 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 deter-
mined 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 on how a module generates
an interrupt, refer to the respective peripheral section.
Note 1: Individual interrupt flag bits are set,
regardless of the status of 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 and CMCON0 registers must
be initialized to configure an analog chan-
nel as a digital input. Pins configured as
analog inputs will read ‘0’. Also, if a LCD
output function is active on an external
interrupt pin, that interrupt function will be
disabled.