Intel 210200-002 manual Cmps BETA,ALPHA Scas Alpha Lods Alpha Stos Beta

ARCHITECTURE AND INSTRUCTIONS

However, the instruction could move either a byte or a word. The assembler must know which is being moved, so it can generate the correct instruction. For this reason, the ASM-86 statement for the MOVS instruc- tion must specify the items that have been moved into SI and D1.

For example:

ALPHA DB?

BETA DB?

MOV	SI,OFFSET ALPHA
MOV	DI,OFFSET BETA
MOVS	BETA,ALPHA

The presence of BETA and ALPHA in the MOVS statement tells the assembler to gen- erate a MOVS instruction that moves bytes, because the TYPE components of both BETA and ALPHA are BYTE. Further, from the SEG components of BETA and ALPHA, the assembler determines if the

Details of ASM-86

Sample One:

Translate the values from input port I into a Gray code and send result to output port 1.

operands of the MOVS instruction are inac- cessible segments. The OFFSET components of ALPHA and BETA are ignored.

Like MOVS, the other four string primitives contain operands, MOVS and CMPS have two operands, while SCAS, LODS, and STOS have one. For example:

CMPS BETA,ALPHA

SCAS ALPHA

LODS ALPHA

STOS BETA

XLAT also requires an operand; the item that was moved into BX to serve as the trans- lation table. The SEG component of this operand enables the assembler to determine if the translation table is in a currently access- ible segment; the OFFSET component is ignored. An example of an XLAT statement is as follows:

MOV BX,OFFSET TABLE

XLAT TABLE

MY_DATA	SEGMENT
GRAY	DB	18H,34H,05H,06H,09H,OAH,OCH,11 H, 12H,14H
MY_DATA	ENDS
MY_CODE	SEGMENT
	ASSUME	CS:MY _CODE, DS:MY _DATA
GO:	MOV	AX,MY_DATA	;establish data segment
	MOV	DS,AX
	MOV	BX,OFFSET GRAY	;translation table into BX
CYCLE:	IN	AL,1	;read in next value
	XLAT	GRAY	;translate it
	OUT	1,AL	;output it
	JMP	CYCLE	;and repeat
	ENDS
	END	GO

2-40