INSTRUCTION DESCRIPTIONS
A - 30 INSTRUCTION SET DETAILS MOTOROLA
Operation: Assembler Syntax:
S+D / 2➞D (parallel move) ADDR S,D (parallel move)
Description: Add the source operand S to one-half the destination operand D and store
the result in the destination accumulator. The destination operand D is arithmetically
shifted one bit to the right while the MS bit of D is held constant prior to the addition oper-
ation. In contrast to the ADDL instruction, the carry bit is always set correctly, and the
overflow bit can only be set by the addition operation and not by an overflow due to the
initial shifting operation. This instruction is useful for efficient divide and decimation in
time (DIT) FFT algorithms.
Example::
ADDR B,A X0,X:(R1)+N1 Y0,Y:(R4)– ;B+A / 2➞A, save X0 and Y0
:
Explanation of Example: Prior to execution, the 56-bit A accumulator contains the
value $80:000000:2468AC, and the 56-bit B accumulator contains the value
$00:013570:000000. The ADDR B,A instruction adds one-half the value in the A accu-
mulator to the value in the B accumulator and stores the 56-bit result in the A accumula-
tor.
ADDR Shift Right and Add Accumulators ADDR
Before Execution After Execution
A A
$80:000000:2468AC
B B
$00:013570:000000 $00:013570:000000
$C0:013570:123456