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8085 PUSH Instruction

  1. Jan 22, 2013 #1
    Is PUSH A Instruction Valid in 8085
    I get this doubt because PUSH and POP always acts on register pairs but only register pairs available in 8085 are BC DE HL there is no register to pair with A so ?
  2. jcsd
  3. Jan 22, 2013 #2
    If you want to push the accumulator you do a PUSH PSW. This pushes the 8-bit accumulator and 8-bits worth of flags. (PSW stands for processor state word).

    I'm showing my age on this one. Why in the world are you interested in 8085?

    Not complaining, I would enjoy reminiscing about this old gem.
  4. Jan 22, 2013 #3
    thanks the_emi_guy :biggrin:
    this damn entrance test, they have mentioned this 1980's 8085 in their test syllabus
    I think its because 8085 is pretty basic and if you master it others can be understood easily :)

    So, PUSH A is invalid instruction in 8085?
  5. Jan 23, 2013 #4
    The actual instruction (opcode) is an F5. PUSH PSW (or PUSH A) are mnemonics that an assembler would recognize and translate into the cooresponding opcode.

    The Intel ICE assemblers that I used (many years ago) recognized only the mnemonic PUSH PSW.
  6. Jan 23, 2013 #5
    For example, the Zilog Z80 processor's assembler used the mnemonic PUSH AF for this same instruction (F5).

    (Z80 would execute 8080/8085 machine code).
  7. Jan 23, 2013 #6
    I'd have to look at my 8085 book. But push a is valid on the Intel 8085 chip. If you google 8085 instruction set there is several pdf books containing the instruction set.
  8. Jan 23, 2013 #7
    Just double checked. My 8080/8085 Assembly Language Programming Manual (1977) uses the mnemonic PUSH PSW. There is no PUSH A in there.

    But the point is PUSH PSW, PUSH A, or PUSH AF are all the same instruction as far as the actual 8085 chip is concerned. The only difference is in what the assembler you are using to assemble your code recognizes.

    All the 8085 chip itself will see is an F5 returned from memory at the program counter address during the M1 (instruction fetch) cycle.
    Last edited: Jan 23, 2013
  9. Jan 23, 2013 #8
    Lol yeah I just dug out my copy from storage you are correct. Been years for myself as well
  10. Jan 23, 2013 #9
    BTW 1970s!
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