Intel 80C188XL, 80C186XL Instruction Set Descriptions, Table C-4.Instruction Set Continued, C-17

INSTRUCTION SET DESCRIPTIONS

Table C-4. Instruction Set (Continued)

Name	Description	Operation	Flags
			Affected
IMUL	Integer Multiply:	When Source Operand is a Byte:	AF ?
	IMUL src	(AX) ← (byte-src) × (AL)	CF
			DF –
	Performs a signed multiplication of the	if
			IF –
		(AH) = sign-extension of (AL)
	source operand and the accumulator.
			OF ¸
		then
	If the source is a byte, then it is	(CF) ← 0	PF ?
	multiplied by register AL, and the
			SF ?
		else
	double-length result is returned in AH
			TF –
		(CF) ← 1
	and AL. If the source is a word, then it
			ZF ?
		(OF) ← (CF)
	is multiplied by register AX, and the
	double-length result is returned in	When Source Operand is a Word:
	registers DX and AX. If the upper half	(DX:AX) ← (word-src) × (AX)
	of the result (AH for byte source, DX
		if
	for word source) is not the sign
		(DX) = sign-extension of (AX)
	extension of the lower half of the
		then
	result, CF and OF are set; otherwise
		(CF) ← 0
	they are cleared. When CF and OF are
		else
	set, they indicate that AH or DX
		(CF) ← 1
	contains significant digits of the result.
		(OF) ← (CF)
	Instruction Operands:
	IMUL reg
	IMUL mem
	IMUL immed
IN	Input Byte or Word:	When Source Operand is a Byte:	AF –
	IN accum, port	(AL) ← (port)	CF –
			DF –
	Transfers a byte or a word from an	When Source Operand is a Word:
			IF –
	input port to the AL register or the AX	(AX) ← (port)
			OF –
	register, respectively. The port number
			PF –
	may be specified either with an
			SF –
	immediate byte constant, allowing
			TF –
	access to ports numbered 0 through
			ZF –
	255, or with a number previously
	placed in the DX register, allowing
	variable access (by changing the value
	in DX) to ports numbered from 0
	through 65,535.
	Instruction Operands:
	IN AL, immed8
	IN AX, DX

NOTE: The three symbols used in the Flags Affected column are defined as follows:

–the contents of the flag remain unchanged after the instruction is executed ¸? the contents of the flag is undefined after the instruction is executed

the flag is updated after the instruction is executed

C-17