dsp56800e Freescale Semiconductor, Inc, dsp56800e Datasheet - Page 484

• Manufacturer Part Number: dsp56800e
• Description: 16-bit Digital Signal Controller Core
• Manufacturer: Freescale Semiconductor, Inc

ILLEGAL
Operation:
Begin illegal instruction exception routine
Description: Normal instruction execution is suspended, and illegal instruction exception processing is initiated.
Usage:
Example:
Explanation of Example: See the description.
Condition Codes Affected:
Instruction Fields:
Instruction Opcodes:
Timing:
Memory:
A-140
ILLEGAL
Operation
ILLEGAL
The interrupt priority level bits (I1 and I0) are set to 11 in the status register. The purpose of the illegal
interrupt is to force the DSC into an illegal instruction exception for test purposes. Executing an
ILLEGAL instruction is a fatal error; the exception routine should indicate this condition and cause the
system to be re-started.
If the ILLEGAL instruction is in a DO loop at the LA and the instruction at the LA – 1 is being inter-
rupted, then LC will be decremented twice. This situation is due to the same mechanism that causes
LC to be decremented twice if JSR, REP, and so on are located at the LA.
Since REP is uninterruptable, the result of repeating an ILLEGAL instruction is that the interrupt is
not taken until after the REP completes. After servicing the interrupt, program control returns to the
address of the second word that follows the ILLEGAL instruction. Of course, the ILLEGAL interrupt
service routine should abort further processing, and the processor should be re-initialized.
The ILLEGAL instruction provides a means for testing the interrupt service routine that is executed
when an illegal instruction is encountered. This capability allows a user to verify that the interrupt ser-
vice routine can correctly recover from an illegal instruction and re-start the application. The
ILLEGAL instruction is not used in normal programming.
ILLEGAL
The condition codes are not affected by this instruction.
4 oscillator clock cycles
1 program word
Operands
Illegal Instruction Interrupt
C
4
DSP56800E Core Reference Manual
W
1
15
1
Execute the illegal instruction exception. This instruction is made avail-
able so that code can be written to test and verify interrupt handlers for
illegal instructions.
1
1
Assembler Syntax:
ILLEGAL
12
0
11
0
1
1
Comments
1
8
7
0
(no parallel move)
0
Freescale Semiconductor
0
ILLEGAL
0
4
1
3
0
1
0
0