Important use of W and Z Registers

W and Z Registers:

These are temporary registers of 8085.
These registers are used to hold 8-bit data during execution of some instructions.
8085 uses these registers internally.
These are not available for programmer.

Use of W and Z Registers:

CALL Instruction:

Whenever the processor wants to execute a subprogram or subroutine, CALL instruction is used to transfer program control to that subroutine.
This instruction transfers the current PC contents onto the stack and loads the given address into PC.
This address is temporarily stored in the W and Z registers.

XCHG Instruction:

This instruction exchanges the contents of H with D and L with E.
At the time of exchange, W and Z registers are used as temporary registers.

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Logical Group Instructions (Part-VI) - RLC, RRC, RAL, RAR

RLC: This instruction rotates the contents of accumulator to the left by one bit. It will shift B0 to B1, B1 to B2,............B7 to B0 as well as to carry flag . Only CY flag is modified. It is a one byte instruction. Implied addressing mode is used. Before execution: After execution: Example: If A = 0101 0111 = 57H and CY = 1 RLC ; Now A = 10101110 = AEH and CY = 0. RRC: This instruction rotates the contents of accumulator to the right by one bit. It will shift B7 to B6, B6 to B5,............B0 to B7 as well as to carry flag. Only CY flag is modified. It is a one byte instruction. Implied addressing mode is used. Before execution: After execution: Example: If A = 1001 1010 = 9AH and CY = 1 RLC ; Now A = 0100 1101 = 4DH and CY = 0. RAL: This instruction rotates the contents of accumulator to the left by one bit along with the carry . It will shift B0 to B1, B1 to B2,............B7 to CY and CY to B0 . Only CY flag is modifi...

Program to exchange the contents of two memory locations

Statement: Exchange the contents of memory locations 2000H and 2001H. Example: Initially, (2000H) = 34H (2001H) = 20H After exchanging, (2000H) = 20H (2001H) = 34H Program 1 using direct addressing instructions: LDA 2000H ; Get the contents of location 2000H into accumulator MOV B, A ; Move the contents of accumulator into register B LDA 2001H ; Get the contents of location 2001H into accumulator STA 2000H ; Store the contents of accumulator into location 2000H MOV A, B ; Move the contents of register B into accumulator STA 2001H ; Store the contents of accumulator into location 2001H HLT ...

Logical Group Instructions (Part-I) - ANA and ANI

ANA R: This instruction logically AND the contents of the specified register with the contents of the accumulator. Register R can be any 8-bit general purpose register like A, B, C, D, E, H and L. The result is stored in the accumulator. S (Sign flag), Z (Zero flag), P (Parity flag) are modified. CY (Carry flag) is reset and AC (Auxiliary Carry flag) is set. It is a one byte instruction. Register addressing mode is used. Example: If A = 0101 1001 = 59H and B = 0000 0011 = 03H ANA B ; This instruction will logically AND the contents of A (59H) with the contents of B (03H) and the result (01H) is stored in A. ANA M: This instruction logically AND the contents of the memory location pointed by HL register pair with the contents of the accumulator. The result is stored in the accumulator. S (Sign flag), Z (Zero flag), P (Parity flag) are modified. CY (Carry flag) is reset and AC (Auxiliary Carry flag) is set. It is a one byte instruction. Register indirect a...

8085 Microprocessors Notes

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