Operations:

Syntax:

Operation:

Operands:

Program Counter:

Opcode

Comment

Stack

MULSU Rd,Rr

R1:R0 = Rd × Rr (signed = signed × unsigned)

16 <= d <= 23, 16 <= r <= 23

PC = PC + 1

000000110ddd0rrr

Description

This instruction performs 8-bit × 8-bit -> 16-bit multiplication of a signed and an unsigned number.

Rd

Rr

R1

R0

->

Product High

Product Low

Multiplicand

Multiplier

8

8

16

The multiplicand Rd and the multiplier Rr are two registers. The multiplicand Rd is a signed number, and the multiplier Rr is unsigned. The 16-bit signed product is placed in R1 (high byte) and R0 (low byte).

This instruction is not available on all devices. Refer to Appendix A.

Status Register (SREG) and Boolean Formula

I

–

T

–

H

–

S

–

V

–

N

–

Z

⇔

~R15 AND ~R14 AND ~R13 AND ~R12 AND ~R11 AND ~R10 AND ~R9 AND ~R8 ANDR7 AND ~R6 AND ~R5 AND ~R4 AND ~R3 AND ~R2 AND ~R1 AND ~R0

Set if the result is 0x0000; cleared otherwise.

C

⇔

R15

R (Result)

R (Result) equals R1,R0 after the operation.

Example: 

;******************************************************************************
;* DESCRIPTION
;* Signed multiply of two 16-bit numbers with 32-bit result.
;* USAGE
;* r19:r18:r17:r16 = r23:r22 * r21:r20
;******************************************************************************
muls16x16_32:
      clr   r2
      muls  r23, r21      ; (signed)ah * (signed)bh
      movw  r18, r0
      mul   r22, r20      ; al * bl
      movw  r16, r0
      mulsu r23, r20      ; (signed)ah * bl
      sbc   r19, r2
      add   r17, r0
      adc   r18, r1
      adc   r19, r2
      mulsu r21, r22      ; (signed)bh * al
      sbc   r19, r2
      add   r17, r0
      adc   r18, r1
      adc   r19, r2
      ret

Words

1 (2 bytes)

Table Cycles

Name

Cycles

AVRe

2

AVRxm

2

AVRxt

2

AVRrc

N/A