The X 86 Microprocessors: Architecture, Programming and Interfacing (8086 to Pentium) 2nd Edition by Pearson

3-36

THE

x86 MICROPROCESSORS

FIRST DB 89H

SECOND DB 0CAH

AVG DB ?

.CODE

.STARTUP

MOV AL, FIRST ;copy FIRST to AL

MOV AH, 0 ;zero-extend

MOV BL, SECOND ;copy SECOND to BL

MOV BH, 0 ;zero-extend

ADD AX, BX ;add the zero extended words

MOV CL, 02 ;load divisor to CL

DIV CL ;divide AX by CL

MOV AVG, AL ;save quotient to AVG

.EXIT

END

Example 3.21 gives a complete program for finding the average of two bytes stored in

memory locations labeled FIRST and SECOND. These are copied to registers AL and

BL and zero extended to convert them to words. Addition of the numbers is then done

as words. This sum, which is the di