PIC18F2331/2431/4331/4431
When the IPEN bit is cleared (default state), the
interrupt priority feature is disabled and interrupts are
10.0 INTERRUPTS
compatible with PIC® mid-range devices. In Compati-
bility mode, the interrupt priority bits for each source
have no effect. INTCON<6> is the PEIE bit, which
enables/disables all peripheral interrupt sources.
INTCON<7> is the GIE bit, which enables/disables all
interrupt sources. All interrupts branch to address
000008h in Compatibility mode.
The PIC18F2331/2431/4331/4431 devices have
multiple interrupt sources and an interrupt priority
feature that allows each interrupt source to be assigned
a high-priority level or a low-priority level. The high-
priority interrupt vector is at 000008h and the low-priority
interrupt vector is at 000018h. High-priority interrupt
events will interrupt any low-priority interrupts that may
be in progress.
When an interrupt is responded to, the global interrupt
enable bit is cleared to disable further interrupts. If the
IPEN bit is cleared, this is the GIE bit. If interrupt priority
levels are used, this will be either the GIEH or GIEL bit.
High-priority interrupt sources can interrupt a low-
priority interrupt. Low-priority interrupts are not
processed while high-priority interrupts are in progress.
There are thirteen registers which are used to control
interrupt operation. These registers are:
• RCON
• INTCON
• INTCON2
• INTCON3
The return address is pushed onto the stack and the
PC is loaded with the interrupt vector address
(000008h or 000018h). 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 bits must be cleared in software before re-enabling
interrupts to avoid recursive interrupts.
• PIR1, PIR2, PIR3
• PIE1, PIE2, PIE3
• IPR1, IPR2, IPR3
It is recommended that the Microchip header files sup-
plied with MPLAB® IDE be used for the symbolic bit
names in these registers. This allows the assembler/
compiler to automatically take care of the placement of
these bits within the specified register.
The “return from interrupt” instruction, RETFIE, exits
the interrupt routine and sets the GIE bit (GIEH or
GIEL if priority levels are used), which re-enables
interrupts.
In general, each interrupt source has three bits to
control its operation. The functions of these bits are:
For external interrupt events, such as the INTx pins or
the PORTB input change interrupt, the interrupt latency
will be three to four instruction cycles. The exact
latency is the same for one or two-cycle instructions.
Individual interrupt flag bits are set, regardless of the
status of their corresponding enable bit or the GIE bit.
• Flag bit to indicate that an interrupt event
occurred
• Enable bit that allows program execution to
branch to the interrupt vector address when the
flag bit is set
• Priority bit to select high priority or low priority
(most interrupt sources have priority bits)
Note:
Do not use the MOVFFinstruction to modify
any of the Interrupt Control registers while
any interrupt is enabled. Doing so may
cause erratic microcontroller behavior.
The interrupt priority feature is enabled by setting the
IPEN bit (RCON<7>). When interrupt priority is
enabled, there are two bits which enable interrupts
globally. Setting the GIEH bit (INTCON<7>) enables all
interrupts that have the priority bit set (high priority).
Setting the GIEL bit (INTCON<6>) enables all
interrupts that have the priority bit cleared (low priority).
When the interrupt flag, enable bit and appropriate
global interrupt enable bit are set, the interrupt will
vector immediately to address 000008h or 000018h
depending on the priority bit setting. Individual
interrupts can be disabled through their corresponding
enable bits.
2010 Microchip Technology Inc.
DS39616D-page 97
MICROCHIP [ MICROCHIP ]
