PIC24HJ12GP201ESLASHML datasheet(51/234 Pages) MICROCHIP

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Preliminary

DS70282B-page 49

PIC24HJ12GP201/202

6.0

INTERRUPT CONTROLLER

The

PIC24HJ12GP201/202

interrupt

controller

reduces the numerous peripheral interrupt request

signals to a single interrupt request signal to the

PIC24HJ12GP201/202 CPU. It has the following

features:

• Up to 8 processor exceptions and software traps

• 7 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

6.1

Interrupt Vector Table

The Interrupt Vector Table is shown in Figure 6-1. The

IVT resides in program memory, starting at location

000004h. The IVT contains 126 vectors consisting of

8 nonmaskable 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.

PIC24HJ12GP201/202 devices implement up to 21

unique interrupts and 4 nonmaskable traps. These are

summarized in Table 6-1 and Table 6-2.

6.1.1

ALTERNATE INTERRUPT VECTOR

TABLE

The Alternate Interrupt Vector Table (AIVT) is located

after the IVT, as shown in Figure 6-1. 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 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.

6.2

Reset Sequence

A device Reset is not a true exception because the

interrupt controller is not involved in the Reset process.

The PIC24HJ12GP201/202 device clears its registers

in response to a Reset, which forces the PC to zero.

The digital signal controller then begins program

execution at location 0x000000. The user application

can use a GOTO instruction at the Reset address which

redirects program execution to the appropriate start-up

routine.

Note:

This data sheet summarizes the features

of the PIC24HJ12GP201/202 devices. It is

not intended to be a comprehensive

reference source. To complement the

information in this data sheet, refer to the

“PIC24H Family Reference Manual”.

Please see the Microchip web site

(www.microchip.com)

for

the

latest

PIC24H

Family

Reference

Manual

chapters.

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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