This is the Solution for your Problem
org 100h
.data
mystr DB 'A','B','C'
RES DB 10 DUP ('$')
.code
; Print the ASSCII for A
lea si,mystr[0]
mov AX,[si]
mov ah,0
LEA SI,RES
CALL HEX2DEC
LEA DX,RES
MOV AH,9
INT 21H
; Print the coma
mov dl,','
mov ah,2
int 21h
; Print the ASSCII for B
lea si,mystr[1]
mov AX,[si]
mov ah,0
LEA SI,RES
CALL HEX2DEC
LEA DX,RES
MOV AH,9
INT 21H
; Print the coma
mov dl,','
mov ah,2
int 21h
; Print the ASSCII for C
lea si,mystr[2]
mov AX,[si]
mov ah,0
LEA SI,RES
CALL HEX2DEC
LEA DX,RES
MOV AH,9
INT 21H
MOV AH,4CH
INT 21H
HEX2DEC PROC NEAR
MOV CX,0
MOV BX,10
LOOP1: MOV DX,0
DIV BX
ADD DL,30H
PUSH DX
INC CX
CMP AX,9
JG LOOP1
ADD AL,30H
MOV [SI],AL
LOOP2: POP AX
INC SI
MOV [SI],AL
LOOP LOOP2
RET
HEX2DEC ENDP
END START
ret
END