Index By Short Displacement: (Sp-Xx), (R2+Xx); Figure 4-8 Address Register Indirect: Indexed By Short Displacement - Motorola DSP56800 Manual

4.2.2.6

Index by Short Displacement: (SP-xx), (R2+xx)

This addressing mode contains the 6-bit short immediate index within the instruction word. This field is
always one-extended to form a negative offset when the SP register is used and is always zero-extended to
form a positive offset when the R2 register is used. The type of arithmetic used to add the short
displacement to R2 or SP is always linear; modulo arithmetic is not allowed. This addressing mode
requires an extra instruction cycle. This reference is classified as an X memory reference. See Figure 4-8.
Indexed by Short Displacement Example
Before Execution
A2 A1
A F E D
35 32 31
15
$7003 X
$7000 X
R2
15
N
15
M01
15
Assembler syntax: X:(Rn+xx), X:(SP-xx)
Additional instruction execution cycles: 1
Additional effective address program words: 0
Figure 4-8. Address Register Indirect: Indexed by Short Displacement
A0
C B A 9 8 7
16 15 0
X Memory
0
X X X
X X X
$7000
0
+
$4567
0
$FFFF
0
Short Immediate Value
from the Instruction Word
Address Generation Unit
: MOVE A1,X:(R2+3)
After Execution
A2 A1
A F E D C B
35 32 31 16 15
X Memory
15
$7003 E D C
$7000 X X X
R2 $7000
15
N $4567
15
M01 $FFFF
15
Addressing Modes
A0
A 9 8 7
0
0
B
X
0
0
0
AA0021
4-15