How to sum multiple BCD numbers in assembly?

Question

I am coding this in Motorola68k simulator. I want my program to execute this task:

• (Address of first element of linked list is saved on address $6000 (longword) followed by length of the list (word) and final result (word))
• Go through linked list (every element of list is containing address of next element (longword) followed by BCD number (byte))
• Sum all BCD numbers of linked list and save the sum in RESULT.

I understand how to go through each element of the list but I'm struggling to add BCD numbers. I want to add in each iteration to numbers and store them in D6, then at the end put D6 in RESULT. Here is my code:

DATA:           EQU     $1500
PROG:           EQU     $1000
LIST:           EQU     $6000

LEN:            EQU     $1500    ;lenght of BCD numbers (all are .B)
NUM1:           EQU     $1510
NUM2:           EQu     $1520

                ORG     LISTA
FIRST           DS.L    1
LENGHT          DS.W    1
RESULT          DS.W    1

                ORG PROG

START:      
                MOVE.L  FIRST, A0
                MOVE.W  LENGHT, D1
                MOVEQ   #0, D2
                MOVEQ   #0, D6
                CLR.W   RESULT
SUM_LOOP:
                CMP.W   #0, D1
                BEQ     DONE
            
                MOVEQ   #0, D3
            
                MOVE.L  (A0)+, A1
                MOVE.B  (A0), D3
                MOVE.B  D3, NUM1
            
                MOVE.L  A1, A0
                MOVE.L  (A1)+, A1
                MOVE.B  (A1), D5
                MOVE.B  D5, NUM2

                CLR.W   D4
                MOVE.B  #1, LEN
                MOVE.B  LEN, D4
                MOVE.W  D4, A5
                LEA NUM1(A5), A3
                LEA NUM2(A5), A4

                SUBQ    #1, D4
                MOVE    #0, CCR

 LOOP:      
                ABCD.B  -(A4), -(A3)
                DBRA    D4, LOOP

                ADD.L   NUM1, D6

                SUBQ.W  #1, D1
                BRA     SUM_LOOP
 DONE:
                MOVE.W  D6, RESULT

                MOVE.B  #9,D0
                TRAP    #15 ; halt simulator

                END  START