PIC24FJ16MC101_12 Datasheet, PDF (71/350 Pages) Microchip Technology – 16-bit Microcontrollers (up to 32 KB Flash and 2 KB SRAM)

PIC24FJ16MC101/102 AND PIC24FJ32MC101/102/104
7.0 INTERRUPT CONTROLLER
Note 1: This data sheet summarizes the features
of the PIC24FJ16MC101/102 and
PIC24FJ32MC101/102/104 family of
devices. It is not intended to be a
comprehensive reference source. To
complement the information in this data
sheet, refer to Section 8. “Interrupts”
(DS39707) in the “PIC24F Family
Reference Manual”, which is available
from the Microchip web site
(www.microchip.com).
2: It is important to note that the
specifications in Section 26.0 “Electri-
cal Characteristics” of this data sheet,
supercede any specifications that may be
provided in PIC24F Family Reference
Manual sections.
3: Some registers and associated bits
described in this section may not be
available on all devices. Refer to
Section 4.0 “Memory Organization” in
this data sheet for device-specific register
and bit information.
The Interrupt Controller reduces the numerous periph-
eral interrupt request signals to a single interrupt
request signal to the PIC24FJ16MC101/102 and
PIC24FJ32MC101/102/104 CPU. It has the following
features:
• Up to eight processor exceptions and software traps
• Seven user-selectable priority levels
• Interrupt Vector Table (IVT) with up to 118 vectors
• A unique vector for each interrupt or exception
source
• Fixed priority within a specified user priority level
• Alternate Interrupt Vector Table (AIVT) for debug
support
• Fixed interrupt entry and return latencies
7.1 Interrupt Vector Table
The Interrupt Vector Table (IVT) is shown in Figure 7-1.
The IVT resides in program memory, starting at location
000004h. The IVT contains 126 vectors consisting of
eight non-maskable trap vectors, plus up to 118
sources of interrupt. In general, each interrupt source
has its own vector. Each interrupt vector contains a 24-
bit-wide address. The value programmed into each
interrupt vector location is the starting address of the
associated Interrupt Service Routine (ISR).
Interrupt vectors are prioritized in terms of their natural
priority. This priority is linked to their position in the
vector table. Lower addresses generally have a higher
natural priority. For example, the interrupt associated
with vector 0 will take priority over interrupts at any
other vector address.
PIC24FJ16MC101/102 and PIC24FJ32MC101/102/
104 devices implement up to 26 unique interrupts and
4 nonmaskable traps. These are summarized in
Table 7-1 and Table 7-2.
7.1.1
ALTERNATE INTERRUPT VECTOR
TABLE
The Alternate Interrupt Vector Table (AIVT) is located
after the IVT, as shown in Figure 7-1. Access to the
AIVT is provided by the ALTIVT control bit
(INTCON2<15>). If the ALTIVT bit is set, all interrupt
and exception processes use the alternate vectors
instead of the default vectors. The alternate vectors are
organized in the same manner as the default vectors.
The AIVT supports debugging by providing a way to
switch between an application and a support
environment without requiring the interrupt vectors to
be reprogrammed. This feature also enables switching
between applications to facilitate evaluation of different
software algorithms at run time. If the AIVT is not
needed, the AIVT should be programmed with the
same addresses used in the IVT.
7.2 Reset Sequence
A device Reset is not a true exception because the
interrupt controller is not involved in the Reset process.
The PIC24FJ16MC101/102 and PIC24FJ32MC101/
102/104 device clears its registers in response to a
Reset, forcing the PC to zero. The microcontroller then
begins program execution at location 0x000000. A
GOTO instruction at the Reset address can redirect
program execution to the appropriate start-up routine.
Note:
Any unimplemented or unused vector
locations in the IVT and AIVT should be
programmed with the address of a default
interrupt handler routine that contains a
RESET instruction.
© 2011-2012 Microchip Technology Inc.
Preliminary
DS39997C-page 71