Motorola DSP56000, 24-Bit Digital Signal Processor manual Signed Multiply, Condition Codes

INSTRUCTION DESCRIPTIONS

MPY MPY

Signed Multiply

Explanation of Example 1: Prior to execution, the 24-bit X1 register contains the value $800000 (–1.0), the 24-bit Y1 register contains the value $C00000, (–0.5), and the 56-bit A accumulator contains the value $00:000000:000000 (0.0). The execution of the MPY – X1,Y1,A instruction multiples the 24-bit signed value in the X1 register by the 24-bit signed value in the Y1 register, negates the 48-bit product, and stores the result in the 56-bit A accumulator (–X1∗Y1=–0.5=$FF:C00000:000000=A).

Condition Codes:

15	14	13	12	11		10	9		8	7	6	5	4	3	2	1		0
LF	DM	T	**		S1	S0		I1	I0	S	L	E	U	N	Z		V	C
				MR									CCR

S — Computed according to the definition in A.5 CONDITION CODE COMPUTATION L — Set if limiting occurred during parallel move

E — Set if the signed integer portion of A or B result is in use

U — Set if A or B result is unnormalized

N — Set if bit 55 of A or B result is set

Z— Set if A or B result equals zero

V — Set if overflow has occurred in A or B result

Note: The definitions of the E and U bits vary according to the scaling mode being used. Refer to Section A.5 CONDITION CODE COMPUTATION for complete details.

Instruction Format 1:
MPY		(±)S1,S2,D
MPY		(±)S2,S1,D
Opcode 1:
23	8	7	4	3	0
		DATA BUS MOVE FIELD	1	Q Q Q	d k	0 0

OPTIONAL EFFECTIVE ADDRESS EXTENSION

MOTOROLA INSTRUCTION SET DETAILS A - 229