Datasheet

56F8033/56F8023 Data Sheet, Rev. 6
56 Freescale Semiconductor
5.3.3 Fast Interrupt Handling
Fast interrupts are described in the DSP56800E Reference Manual. The interrupt controller recognizes
Fast Interrupts before the core does.
A Fast Interrupt is defined (to the ITCN) by:
1. Setting the priority of the interrupt as level 2, with the appropriate field in the IPR registers
2. Setting the FIMn register to the appropriate vector number
3. Setting the FIVALn and FIVAHn registers with the address of the code for the
Fast Interrupt
When an interrupt occurs, its vector number is compared with the FIM0 and FIM1 register values. If a
match occurs, and it is a level 2 interrupt, the ITCN handles it as a Fast Interrupt. The ITCN takes the vector
address from the appropriate FIVALn and FIVAHn registers, instead of generating an address that is an
offset from the VBA.
The core then fetches the instruction from the indicated vector address and if it is not a JSR, the core starts
its Fast Interrupt handling.
11 Priority 2 or 3 Priority 3
Table 5-2 Interrupt Priority Encoding
IPIC_VALUE[1:0]
Current Interrupt
Priority Level
Required Nested
Exception Priority