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Instruction Set Description
4.6.2.37 RETI
RETI
Return from interrupt
RETI
Syntax
Operation
@SP
→
SR.15:0
Restore saved SR with PC.19:16
SP + 2
→
SP
@SP
→
PC.15:0
Restore saved PC.15:0
SP + 2
→
SP
Housekeeping
Description
The SR is restored to the value at the beginning of the interrupt service routine. This
includes the four MSBs of the PC.19:16. The SP is incremented by two afterward.
The 20-bit PC is restored from PC.19:16 (from same stack location as the status bits)
and PC.15:0. The 20-bit PC is restored to the value at the beginning of the interrupt
service routine. The program continues at the address following the last executed
instruction when the interrupt was granted. The SP is incremented by two afterward.
Status Bits
N:
Restored from stack
C:
Restored from stack
Z:
Restored from stack
V:
Restored from stack
Mode Bits
OSCOFF, CPUOFF, and GIE are restored from stack.
Example
Interrupt handler in the lower 64 K. A 20-bit return address is stored on the stack.
INTRPT
PUSHM.A
#2,R14
; Save R14 and R13 (20-bit data)
...
; Interrupt handler code
POPM.A
#2,R14
; Restore R13 and R14 (20-bit data)
RETI
; Return to 20-bit address in full memory range
170
CPUX
SLAU272C – May 2011 – Revised November 2013
Copyright © 2011–2013, Texas Instruments Incorporated