dsPIC30F Family Reference Manual
DS70053C-page 6-42 © 2004 Microchip Technology Inc.
6.5 Interrupt Setup Procedures
6.5.1 Initialization
The following steps describe how to configure a source of interrupt:
1. Set the NSTDIS Control bit (INTCON1<15>) if nested interrupts are not desired.
2. Select the user assigned priority level for the interrupt source by writing the control bits in
the appropriate IPCx Control register. The priority level will depend on the specific
application and type of interrupt source. If multiple priority levels are not desired, the IPCx
register control bits for all enabled interrupt sources may be programmed to the same
non-zero value.
3. Clear the interrupt flag status bit associated with the peripheral in the associated IFSx
Status register.
4. Enable the interrupt source by setting the interrupt enable control bit associated with the
source in the appropriate IECx Control register.
6.5.2 Interrupt Service Routine
The method that is used to declare an ISR and initialize the IVT with the correct vector address
will depend on the programming language (i.e., C or assembler) and the language development
tool suite that is used to develop the application. In general, the user must clear the interrupt flag
in the appropriate IFSx register for the source of interrupt that the ISR handles. Otherwise, the
ISR will be re-entered immediately after exiting the routine. If the ISR is coded in assembly
language, it must be terminated using a RETFIE instruction to unstack the saved PC value, SRL
value, and old CPU priority level.
6.5.3 Trap Service Routine
A Trap Service Routine (TSR) is coded like an ISR, except that the appropriate trap status flag
in the INTCON1 register must be cleared to avoid re-entry into the TSR.
6.5.4 Interrupt Disable
All user interrupts can be disabled using the following procedure:
1. Push the current SR value onto the software stack using the PUSH instruction.
2. Force the CPU to priority level 7 by inclusive ORing the value 0xE0 with SRL.
To enable user interrupts, the POP instruction may be used to restore the previous SR value.
Note that only user interrupts with a priority level of 7 or less can be disabled. Trap sources
(level 8-level 15) cannot be disabled.
The DISI instruction provides a convenient way to disable interrupts of priority levels 1-6, for a
fixed period of time. Level 7 interrupt sources are not disabled by the DISI instruction.
Note: At a device Reset, the IPC registers are initialized, such that all user interrupt
sources are assigned to priority level 4.
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