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I'm trying to make my C programming exciting by learning assembly programming.

I've encountered an image of flag registers in 8085 assembly programming. In that image blocks are named from d0-d7(numerals in subscript). Why are they named 'd'? Is this arbitrarily chosen? There is another register with the name 'D', are both same or different?

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If the image you saw is like this one, D0-D7 imply bit positions in the status register, called F (for flags) when part of the AF register pair. The Ds are misleading because they imply some (nonexistent) relationship to the D register or the data pins (which are multiplexed with the address lines and are actually called AD0-AD7).

Describing bit positions for the status flags doesn't mean much of anything for most people because the only instructions that operate on F deal with a single bit at a time (conditional jumps, conditional subroutine calls and the instructions that set and clear the carry flag). The only way to operate on the flags as a whole would be to transfer them to or from another register by way of the stack.

  • Yes, that's how the image looked. Thanks for replying. – want2code Feb 18 '15 at 17:16
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Yes there is difference

d0-d7 are 8 bit data bus and D is one of the register in 8085

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In 8086 assembly that I learnt in Uni, D stood for data. There were four main register groups, AX, BX, CX, DX. Accumulator, Base, Count, and Data. And I suspect it didn't hurt that they were ABCD.

  • The register structure on the 8086 was not the same as the 8085. – Blrfl Feb 18 '15 at 13:57

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