Post-Decrement By 1: (Rn)-, (Sp); Figure 4-5 Address Register Indirect: Post-Decrement - Motorola DSP56800 Manual

Address Generation Unit
4.2.2.3

Post-Decrement by 1: (Rn)-, (SP)-

The address of the operand is in the address register Rn or SP. After the operand address is used, it is
decremented by one and stored in the same address register. The type of arithmetic (linear or modulo) used
to increment Rn is determined by M01 for R0 and R1 and is always linear for R2, R3, and SP. The N
register is ignored. This reference is classified as a memory reference. See Figure 4-5.
Before Execution
B2 B1
B 0 6 5
35 32 31
15
$4735 X
$4734 X
R1
15
N
15
M01
15
Assembler syntax: X:(Rn)-, X:(SP)-
Additional instruction execution cycles: 0
Additional effective address program words: 0
Figure 4-5. Address Register Indirect: Post-Decrement
4-12
Post-Decrement Example
B0
4 3 F E D C
16 15 0
X Memory
0
X X X
X X X
$4735
0
(n/a)
0
$FFFF
0
DSP56800 Family Manual
: MOVE B,X:(R1)-
After Execution
B2 B1
B 0 6 5 4 3
35 32 31 16 15
X Memory
15
$4735 6 5 4
$4734 X X X
R1 $4734
15
N (n/a)
15
M01 $FFFF
15
B0
F E D C
0
0
3
X
0
0
0
AA0018