NASP
6-243
NASP Unalign Stack Pointer
SYNTAX OPTIONS OPCODE OBJMODE RPT CYC
NASP 0111 0110 0001 0111 X − 1
Operands None
Description If the SPA bit is 1, the NASP instruction decrements the stack pointer (SP) by
1 and then clears the SPA status bit. This undoes a stack pointer alignment
performed earlier by the ASP instruction. If the SPA bit is 0, then the NASP
instruction performs no operation.
if( SPA = 1 )
{
SP = SP − 1;
SPA = 0;
}
Flags and
Modes
PSA If (SPA = 1), then SPA is cleared.
Repeat This instruction is not repeatable. If this instruction follows the RPT
instruction, it resets the repeat counter (RPTC) and executes only once.
Example ; Alignment of stack pointer in interrupt service routine:
; Vector table:
INTx: .long INTxService ; INTx interrupt vector
.
.
INTxService:
ASP ; Align stack pointer
.
.
.
NASP ; Re−align stack pointer
IRET ; Return from interrupt.
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