DSPIC30F6010A MICROCHIP [Microchip Technology], DSPIC30F6010A Datasheet - Page 45

• Manufacturer Part Number: DSPIC30F6010A
• Description: High-Performance, 16-bit Digital Signal Controllers
• Manufacturer: MICROCHIP [Microchip Technology]

5.4
All interrupt event flags are sampled in the beginning of
each instruction cycle by the IFSx registers. A pending
Interrupt Request (IRQ) is indicated by the flag bit
being equal to a ‘1’ in an IFSx register. The IRQ will
cause an interrupt to occur if the corresponding bit in
the Interrupt Enable register (IECx) is set. For the
remainder of the instruction cycle, the priorities of all
pending interrupt requests are evaluated.
If there is a pending IRQ with a priority level greater
than the current processor priority level in the IPL bits,
the processor will be interrupted.
The processor then stacks the current program counter
and the low byte of the processor STATUS register
(SRL), as shown in
STATUS register contains the processor priority level at
the time prior to the beginning of the interrupt cycle.
The processor then loads the priority level for this inter-
rupt into the STATUS register. This action will disable
all lower priority interrupts until the completion of the
Interrupt Service Routine.
FIGURE 5-2:
The RETFIE (Return from Interrupt) instruction will
unstack the program counter and STATUS registers to
return the processor to its state prior to the interrupt
sequence.
© 2011 Microchip Technology Inc.
0x0000
Note 1: The user can always lower the priority
2: The IPL3 bit (CORCON<3>) is always
Interrupt Sequence
15
SRL IPL3 PC<22:16>
level by writing a new value into SR. The
Interrupt Service Routine must clear the
interrupt flag bits in the IFSx register
before lowering the processor interrupt
priority in order to avoid recursive
interrupts.
clear when interrupts are being pro-
cessed. It is set only during execution of
traps.
<Free Word>
PC<15:0>
Figure
INTERRUPT STACK
FRAME
5-2. The low byte of the
0
W15 (before CALL)
W15 (after CALL)
PUSH : [W15++]
POP
: [--W15]
dsPIC30F6010A/6015
5.5
In program memory, the Interrupt Vector Table (IVT) is
followed by the Alternate Interrupt Vector Table (AIVT),
as shown in
Table is provided by the ALTIVT bit in the INTCON2
register. If the ALTIVT bit is set, all interrupt and excep-
tion 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 required, the program memory allo-
cated to the AIVT may be used for other purposes.
AIVT is not a protected section and may be freely
programmed by the user.
5.6
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.
5.7
The interrupt controller supports 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 five bits, INT0EP-INT4EP, that
select the polarity of the edge detection circuitry.
5.8
The interrupt controller may be used to wake-up the
processor from either Sleep or Idle modes, 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 will wake-up from Sleep or
Idle and begin execution of the Interrupt Service
Routine (ISR) needed to process the interrupt request.
Alternate Vector Table
Fast Context Saving
External Interrupt Requests
Wake-up from Sleep and Idle
Figure
5-1. Access to the Alternate Vector
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