8085 program to find 2's complement of the contents of Flag Register

In this program we will see how to find 2's complement of the content of flag register.

Problem Statement

Write 8085 Assembly language program to find 2's complement of the content of flag register.

Discussion

We cannot access the total flag register directly. To use them we have to push the PSW(Accumulator-Flag) into stack, and then pop it to another register pair, then after complementing the LS byte of that register pair, we have to push it again into the stack, and then pop it to PSW to get it into Flag bits.

Input

Here we are not putting any input directly. If the flag bits are (0100 0001), then the program will generate the complement of it.

Flow Diagram

Program

Address	HEX Codes	Mnemonics	Comments
F000	31, 00, 90	LXI SP,9000H	Initialize the stack pointer
F003	F5	PUSH PSW	Push A and F content to Stack
F004	C1	POP B	Pop from stack and store to BC
F005	79	MOV A,C	Take the number from C to A
F006	2F	CMA	Complement the accumulator
F007	4F	MOV C,A	Store A to C
F008	0C	INR C	Increase C by1 to get 2's complement
F009	C5	PUSH B	Push BC into stack
F00A	F1	POP PSW	Pop stack content to A and F
F00B	76	HLT	Terminate the program