PIC24F16KA102 datasheet(63/278 Pages) MICROCHIP

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DS39927C-page 63

PIC24F16KA102 FAMILY

8.0

INTERRUPT CONTROLLER

The PIC24F interrupt controller reduces the numerous

peripheral interrupt request signals to a single interrupt

request signal to the 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

• 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

8.1

Interrupt Vector (IVT) Table

The IVT is displayed in Figure 8-1. The IVT resides in

the 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 is linked to their position in the vector table.

All other things being equal, lower addresses have a

higher natural priority. For example, the interrupt

associated with Vector 0 will take priority over interrupts

at any other vector address.

PIC24F16KA102

family

devices

implement

non-maskable traps and unique interrupts; these are

summarized in Table 8-1 and Table 8-2.

8.1.1

ALTERNATE INTERRUPT VECTOR

TABLE (AIVT)

The Alternate Interrupt Vector Table (AIVT) is located

after the IVT, as displayed in Figure 8-1. Access to the

AIVT is provided by the ALTIVT control bit

(INTCON2<15>). If the ALTIVT bit is set, all interrupt

and exception processes will 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 emulation and debugging efforts by

providing a means to switch between an application

and a support environment without requiring the

interrupt vectors to be reprogrammed. This feature also

enables switching between applications for 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.

8.2

Reset Sequence

A device Reset is not a true exception because the

interrupt controller is not involved in the Reset process.

The PIC24F devices clear their registers in response to

a Reset, which forces the Program Counter (PC) to

zero. The microcontroller then begins program execu-

tion at location, 000000h. The user programs a GOTO

instruction at the Reset address, which redirects the

program execution to the appropriate start-up routine.

Note:

This data sheet summarizes the features

of this group of PIC24F devices. It is not

intended

comprehensive

reference source. For more information

on the Interrupt Controller, refer to the

“PIC24F

Family

Reference

Manual”

Section 8. “Interrupts”

(DS39707).

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.

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