DATA SEGMENT
BUF1 DB 34H
BUF2 DB 2AH
SUM  DB ?
DATA ENDS

CODE SEGMENT
Assume CS:CODE, DS:DATA
START:   MOV Ax,DATA
       MOV DS, AX
       MOV AL, BUF1
       Add AL, BUF2
       MOV SUM, AL
       MOV AH, 4CH
       INT 21H
CODE ENDS
       END START

为什么在masmplus中编译有错误