SUBSTRACTION WITH BORROW - Microprocessor

.DOSSEG
.MODEL SMALL
.STACK
.DATA
NUM1 DB 93H
NUM2 DB 94H
RES DB ?
.CODE
START:
MOV AX,@DATA
MOV DS,AX
MOV AX,0000H
MOV AL,NUM1
STB
SBB AL,NUM2
MOV RES,AL
INT 21H
END START
END

RES:
0E32:0008  FE