Motorola 24-Bit Digital Signal Processor, DSP56000 manual Signed Multiply Instruction Fields S1∗S2

INSTRUCTION DESCRIPTIONS

MPY MPY

Signed Multiply

Instruction Fields 1:
S1∗S2	Q	Q	Q	Sign	k	D	d
X0 X0	0	0	0	+	0	A	0
Y0 Y0	0	0	1	–	1	B	1
X1 X0	0	1	0
Y1 Y0	0	1	1
X0 Y1	1	0	0
Y0 X0	1	0	1
X1 Y0	1	1	0
Y1 X1	1	1	1

Note: Only the indicated S1∗S2 combinations are valid. X1∗X1 and Y1∗Y1 are not valid.

Timing: 2+mv oscillator clock cycles

Memory: 1+mv program words

Example 2:

:
MPY X1,		#9, A
:
			Before Execution
	X1
		$654321

;

X1

After Execution

$654321

A

$00:000000:000000

A

$00:0032A1:908000

Explanation of Example 2: The content of X1 is multiplied by 2-9and the result is

placed in the A accumulator. The net effect of this operation is to divide the content of X1 by 29 and place the result in the accumulator. An alternate interpretation is that X1 is right shifted 9 places and filled with the sign bit (0 for a positive number and 1 for a neg- ative number) and then the result is placed in the accumulator.

A - 230 INSTRUCTION SET DETAILS MOTOROLA