8085 program to add even parity to a string of 7 bit ASCII characters.

Here we will see how to add even parity to 7-bit ASCII string using 8085.

Problem Statement

Write a program to add even parity to a string of 7 bit ASCII characters. The length of the string is in memory location 8040 H and the string itself begins at memory location 8041 H. Place even parity in the most significant bit of each character.

Discussion

8085 has parity flat. that flag will be used to check and assign parity with each ASCII character. At first we will clear the most significant bit by masking the number with 7FH. Then use OR instruction, as this effects on parity flag. If the parity is even, then skip, otherwise set most significant bit as 1. This process will repeat until the string is not exhausted.

Input

Address	Data
…	…
8040	06
8041	7F
8042	55
8043	D5
8044	FF
8045	13
8046	88
…	…

Flow Diagram

Program

Address	HEX Codes	Labels	Mnemonics	Comments
8000	21, 40. 80	START:	LXI H, 8040 H	H 8040 H Counter pointer
8003	4E		MOV C, M	C (HL) counter
8004	23	LOOP:	INX H	HL HL + 1
8005	7E		MOV A, M	A (HL); get a word
8006	E6, 7F		ANI 7F H	Mask most significant bit=0 since it will be used for parity bit
8008	B7		ORA A	To check for parity (ORA affects S, Z, P)
8009	EA, 0E, 80		JPE DOWN	Is parity even, if yes go to down
800C	F6, 80		ORI 80 H	Add 1 as most significant bit
800E	77	DOWN:	MOV M, A	Store result
800F	0D		DCR C	Counter = Counter – 1
8010	C2, 04, 80		JNZ LOOP	Is C = 0? If no then go to loop
8013	76		HLT	Stop