PIC18F-LF1XK50 MICROCHIP [Microchip Technology], PIC18F-LF1XK50 Datasheet - Page 67

• Manufacturer Part Number: PIC18F-LF1XK50
• Description: 20-Pin USB Flash Microcontrollers
• Manufacturer: MICROCHIP [Microchip Technology]

7.0
The PIC18F/LF1XK50 devices have multiple interrupt
sources and an interrupt priority feature that allows
most interrupt sources to be assigned a high priority
level or a low priority level. The high priority interrupt
vector is at 0008h and the low priority interrupt vector is
at 0018h. A high priority interrupt event will interrupt a
low priority interrupt that may be in progress.
There are ten registers which are used to control
interrupt operation. These registers are:
• RCON
• INTCON
• INTCON2
• INTCON3
• PIR1, PIR2
• PIE1, PIE2
• IPR1, IPR2
It is recommended that the Microchip header files sup-
plied with MPLAB
names in these registers. This allows the assembler/
compiler to automatically take care of the placement of
these bits within the specified register.
In general, interrupt sources have three bits to control
their operation. They are:
• Flag bit to indicate that an interrupt event
• Enable bit that allows program execution to
• Priority bit to select high priority or low priority
7.1
When the IPEN bit is cleared (default state), the interrupt
priority feature is disabled and interrupts are compatible
with PIC
Compatibility mode, the interrupt priority bits of the IPRx
registers have no effect. The PEIE bit of the INTCON
register is the global interrupt enable for the peripherals.
The PEIE bit disables only the peripheral interrupt
sources and enables the peripheral interrupt sources
when the GIE bit is also set. The GIE bit of the INTCON
register is the global interrupt enable which enables all
non-peripheral interrupt sources and disables all
interrupt sources, including the peripherals. All interrupts
branch to address 0008h in Compatibility mode.
 2010 Microchip Technology Inc.
occurred
branch to the interrupt vector address when the
flag bit is set
INTERRUPTS
Mid-Range Compatibility
®
microcontroller mid-range devices. In
®
IDE be used for the symbolic bit
Preliminary
7.2
The interrupt priority feature is enabled by setting the
IPEN bit of the RCON register. When interrupt priority
is enabled the GIE and PEIE global interrupt enable
bits of Compatibility mode are replaced by the GIEH
high priority, and GIEL low priority, global interrupt
enables. When set, the GIEH bit of the INTCON regis-
ter enables all interrupts that have their associated
IPRx register or INTCONx register priority bit set (high
priority). When clear, the GIEL bit disables all interrupt
sources including those selected as low priority. When
clear, the GIEL bit of the INTCON register disables only
the interrupts that have their associated priority bit
cleared (low priority). When set, the GIEL bit enables
the low priority sources when the GIEH bit is also set.
When the interrupt flag, enable bit and appropriate
global interrupt enable bit are all set, the interrupt will
vector immediately to address 0008h for high priority,
or 0018h for low priority, depending on level of the
interrupting source’s priority bit. Individual interrupts
can be disabled through their corresponding interrupt
enable bits.
7.3
When an interrupt is responded to, the global interrupt
enable bit is cleared to disable further interrupts. The
GIE bit is the global interrupt enable when the IPEN bit
is cleared. When the IPEN bit is set, enabling interrupt
priority levels, the GIEH bit is the high priority global
interrupt enable and the GIEL bit is the low priority
global interrupt enable. High priority interrupt sources
can interrupt a low priority interrupt. Low priority
interrupts are not processed while high priority
interrupts are in progress.
The return address is pushed onto the stack and the
PC is loaded with the interrupt vector address (0008h
or 0018h). Once in the Interrupt Service Routine, the
source(s) of the interrupt can be determined by polling
the interrupt flag bits in the INTCONx and PIRx
registers. The interrupt flag bits must be cleared by
software before re-enabling interrupts to avoid
repeating the same interrupt.
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.
For external interrupt events, such as the INT pins or
the PORTB interrupt-on-change, the interrupt latency
will be three to four instruction cycles. The exact
latency is the same for one-cycle or two-cycle
Interrupt Priority
Interrupt Response
PIC18F/LF1XK50
DS41350E-page 67