Friday, 29 July 2011

8085 Instruction set - Branch Instructions

             The branching instructions alter the normal sequential program either conditionaly or unconditionally.

As formerly seen in my previous posts in this Series, we divided the Series into four parts:


     JMP :
          This instruction is used to jump from one set of programs to another set
                e.g:   In a 8 bit multiplication program, JN2 LOOP it means that if no zero results in previous arithmetic operation, it will jump to LOOP.
    CALL :
          This instruction is used to call the function.
                e.g:   CALL DIV,CALL SUB etc..
    RET :
          This instruction is used to return to the program after doing some manipulation for a program to succeed.

          Here we are going to discuss some instructions which we use with jump instruction.
The instructions are

        NZ Not Zero (Z = 0)
        Z    Zero (Z = 1)
        NC No Carry (C = 0)
        C    Carry (C = 1)
        PO Parity Odd (P = 0)
        PE Parity Even (P = 1)
        P   Plus (S = 0)
        M  Minus (S = 1)

        Jumps Calls Returns
        C CC RC (Carry)
        INC CNC RNC (No Carry)
        JZ CZ RZ (Zero)
        JNZ CNZ RNZ (Not Zero)
        JP CP RP (Plus)
        JM CM RM (Minus)
        JPE CPE RPE (Parity Even)
        JP0 CPO RPO (Parity Odd)
        Two other instructions can affect a branch by replacing the contents or the program counter:

        PCHL Move H & L to Program Counter
        RST    Special Restart Instruction Used with Interrupts

Stack I/O, and Machine Control Instructions:
    The following instructions affect the Stack and/or Stack Pointer:

        PUSH  Push Two bytes of Data onto the Stack
        POP     Pop Two Bytes of Data off the Stack
        XTHL Exchange Top of Stack with H & L
        SPHL  Move content of H & L to Stack Pointer

The I/0 instructions are as follows:
        IN     Initiate Input Operation
        OUT Initiate Output Operation

The Machine Control instructions are as follows:
        EI      Enable Interrupt System
        DI     Disable Interrupt System
        HLT Halt
        NOP No Operation


I think now u may have realized why i was stressing you to complete the series of post. Good luck.

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