8085 program with a subroutine to add ten packed BCD numbers.

Here we will see how to add ten packed BCD numbers using 8085.

Problem Statement

A set of ten packed BCD numbers is stored in the memory location starting from 8040H to 8049H.

Write a program with a subroutine to add these numbers in BCD. If a carry is generated save it to register B, and adjust it to BCD. The final sum will be less than 9999BCD. Store the sum at locations 8060H and 8061H.
Write a second subroutine to unpack the BCD sum stored in registers A and B, and store them in the OutputBuffer memory starting at 8062H. The most significant digit (BCD4) should be stored at 8065H and the least significant digit (BCD1) at 8062H.

Discussion

The numbers are present at 8040 onwards. As the B will store the carry, we have to clear the B first. In the first phase we have to take the number from memory, then add them as BCD numbers, and store them accordingly. In the next phase the Unpacking task will be completed. In that part we are taking the 16-bit BCD number then break it into 4 digits. Then store them into given location.

Input

Address	Data
…	…
8040	12
8041	23
8042	42
8043	55
8044	10
8045	99
8046	35
8047	45
8048	76
8049	81
…	…

Flow Diagram

Program

Address	HEX Codes	Labels	Mnemonics	Comments
8000	21, 40, 80		LXI H 8040H	Initialize pointer with the first location of IN-BUFFER
8003	0E, 0A		MVI C 0AH	Initialize counter with the number of data to be add
8005	AF		XRA A	Clear the contents of the accumulator and the Reg. B
8006	47		MOV B, A
8007	CD, 23, 80	NEXTBCD:	CALL BCDADD	A subroutine that add BCD numbers
800A	23		INX H	Go to next location
800B	0D		DCR C	Decrement count until 0 is reached
800C	C2, 07, 80		JNZ NEXTBCD
800F	32, 60, 80		STA 8060 H	Store the result byte available in A
8012	57		MOV D, A	Temporarily D = A
8013	78		MOV A, B	Putting B in A
8014	32, 61, 80		STA 8061 H	To store it in OUT-BUFFER
8017	7A		MOV A, D	Restoring back A
8018	21, 62, 80		LXI H 8062H	Initialize pointer with the last location of OUT-BUFFER
801B	CD, 2E, 80		CALL UNPAK	A subroutine that separates two nibbles from a packed BCD number
801E	78		MOV A, B	Copy B to A
801F	CD, 2E, 80		CALL UNPAK	A subroutine that separates two nibbles from a packed BCD number
8022	76		HLT	Terminate the program
8023	86	BCDADD:	ADD M	Add the contents of the memory location specified by the HL register pair with A
8024	27		DAA	Decimal adjust accumulator
8025	D0		RNC	If no carry is produced then return to the calling program
8026	57		MOV D, A	Copy A to D
8027	78		MOV A, B	If a carry is produced then adjust the contents of the Reg. B
8028	C6. 01		ADI 01H
802A	27		DAA
802B	47		MOV B, A
802C	7A		MOV A, D	Copy D to A
802D	C9		RET	Return to the calling program
802E	57	UNPAK:	MOV D, A	Copy A to D
802F	E6, 0F		ANI 0FH	Mask off the most significant four bits
8031	77		MOV M, A	Writing A to the memory
8032	23		INX H	Go to next location
8033	7A		MOV A, D	Copy D to A
8034	E6, F0		ANI F0H	Mask off the least significant four bits
8036	0F		RRC	Rotate accumulator 4 times to get the first BCD digit
8037	0F		RRC
8038	0F		RRC
8039	0F		RRC
803A	77		MOV M, A	Writing A to the memory
803B	23		INX H	Go to next location
803C	C9		RET	Return to the calling program