PIC24HJ12GP201 Datasheet, PDF (51/234 Pages) Microchip Technology – High-Performance, 16-Bit Microcontrollers

PIC24HJ12GP201/202
6.0 INTERRUPT CONTROLLER
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.
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:
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.
© 2007 Microchip Technology Inc.
Preliminary
DS70282B-page 49