8085 Block movement with overlap

In this program, we will see how to move blocks of data from one place to another.

Problem Statement

Write 8085 Assembly language program to move a data block. The blocks are assumed to be overlapping. The block size is given, the block is starting from Xand we have to move it to the location Y.

Discussion

The overlapping block movement is tricky; we need to use some special tricks to move a block in overlapping address locations. Here the block is starting at position X, we have to move it to position Y. The location Y is inside the block. So Y < X + block size.

In this program, the data are stored at location 8010H, and we will place it 8014H. The block size is stored at location 8000H.

To move a block into some overlapping locations, we will start from the end element of the block. So at first the last element of the block is moved, then the previous bytes are moved.  

Input

Address	Data
. . .	. . .
8000	07
. . .	. . .
8010	11
8011	22
8012	33
8013	44
8014	55
8015	66
8016	77
. . .	. . .

Flow Diagram

Program

Address	HEX Codes		Labels	Mnemonics	Comments
F000		21, 00, 80		LXI H, 8000H	Load the location to find block size
F003		4E		MOV C, M	store block size into C register
F004		06, 00		MVI B,00H	clear B register
F006		21,10, 80		LXI H,8010H	load the source address to HL pair
F009		11, 14, 80		LXI D, 8014H	load the destination address to DE pair
F00C		09		DAD B	Add BC with HL to point next location of the end of the source block
F00D		2B		DCX H	Point last element
F00E		EB		XCHG	Swap DE and HL pair content
F00F		09		DAD B	Add BC with HL to point next location of the end of dest block
F010		2B		DCX H	Point last element
F011		EB		XCH G	Swap DE and HL pair content
F012		7E	LOOP	MOV A, M	Load Acc with the memory element
F013		12		STAX D	Store acc content to the memory pointed by D
F014		1B		DCX D	Decrease DE register pair
F015		2B		DCX H	Decrease HL register pair
F016		0D		DCR C	Decrease C register
F017		C2, 12, F0		JNZ LOOP	Jump to Loop
F01A		76		HLT	Terminate the program

Output:

Address	Data
. . .	. . .
8000	07
. . .	. . .
8010	11
8011	22
8012	33
8013	44
8014	11
8015	22
8016	33
8017	44
8018	55
8019	66
801A	77