Datasheet

dsPIC30F3014/4013
DS70138G-page 64  2010 Microchip Technology Inc.
8.5 Alternate Vector Table
In program memory, the Interrupt Vector Table (IVT) is
followed by the Alternate Interrupt Vector Table (AIVT),
as shown in Figure 8-1. Access to the alternate vector
table is provided by the ALTIVT bit in the INTCON2 reg-
ister. 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 sup-
ports 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 required, the program memory
allocated to the AIVT may be used for other purposes.
AIVT is not a protected section and may be freely
programmed by the user.
8.6 Fast Context Saving
A context saving option is available using shadow reg-
isters. Shadow registers are provided for the DC, N,
OV, Z and C bits in SR, and the registers, W0 through
W3. The shadows are only one level deep. The shadow
registers are accessible using the PUSH.S and POP.S
instructions only.
When the processor vectors to an interrupt, the
PUSH.S instruction can be used to store the current
value of the aforementioned registers into their
respective shadow registers.
If an ISR of a certain priority uses the PUSH.S and
POP.S instructions for fast context saving, then a
higher priority ISR should not include the same instruc-
tions. Users must save the key registers in software
during a lower priority interrupt if the higher priority ISR
uses fast context saving.
8.7 External Interrupt Requests
The interrupt controller supports up to five external
interrupt request signals, INT0-INT4. These inputs are
edge sensitive; they require a low-to-high or a high-to-
low transition to generate an interrupt request. The
INTCON2 register has three bits, INT0EP-INT2EP, that
select the polarity of the edge detection circuitry.
8.8 Wake-up from Sleep and Idle
The interrupt controller may be used to wake-up the
processor from either Sleep or Idle mode, if Sleep or
Idle mode is active when the interrupt is generated.
If an enabled interrupt request of sufficient priority is
received by the interrupt controller, then the standard
interrupt request is presented to the processor. At the
same time, the processor wakes up from Sleep or Idle
and begins execution of the Interrupt Service Routine
(ISR) needed to process the interrupt request.