Intel 210200-002 manual Multiplymul, MUL source

MUL

MULTIPLYMUL

Operation:	Flags Affected:
(DES) +- (LSRC) * (RSRC), where *	CF, OF.
is unsigned multiply	AF, PF, SF, ZF undefined
if (EXT) = 0 then (CF) +- 0
else (CF) +-1;
(OF) +- (CF)

Description:

MUL source

MUL (Multiply) performs an unsigned multi- plication of the source operand and the accum- ulator. If the source is a byte, then it is multiplied by register AL, and the double- length result is returned in AH and AL. If the source operand is a word, then it is multiplied by register AX, and the double-length result is returned in registers DX and AX. The oper-

ands are treated as unsigned binary numbers (see AAM). If the upper half of the result (AH for byte source, DX for word source) is non- zero, CF and OF are set; otherwise they are cleared. When CF and OF are set, they indi- cate that AH or DX contains significant digits of the result. The content of AF, PF, SF and ZF is undefined following execution of MUL.

Encoding:

11111 011 w 1mod 1 00 rIm 1

if w = 0 then LSRC = AL, RSRC = EA, DEST = AX, EXT = AH else LSRC = AX, RSRC = EA, DEST = DX:AX, EXT = OX

MUL Operands	Clocks	Transfers Bytes MUL Coding Example
reg8	70-77	-	2	MUL BL
reg16	118-113	-	2	MULCX
mem8	(76-83)+ EA	1	2-4	MUL MONTH [SI]
mem16	(128-143) + EA	1	2-4	MUL BAUD_RATE

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