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Thread: 8085 vs 80c85

  1. #1

    Default 8085 vs 80c85

    Is there any difference between them, besides the CMOS 8085 is low power? Do all variants of the 80c85 support all the 8085 undocumented instructions? I have found information that some 80c85 versions (eg. Tundra Semiconductor Corporation's CA80C85B) have additional functionality, eg. extra machine code instructions. However, after checking data sheet, I found only the same well known the 8085's ten additional instructions. Is it true that it is impossible to add more instructions to the 8085? Thank you.

  2. #2
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    The undocumented instructions are the same in both. Intel originally distributed the information about the added instructions as an internal company memo. But they're there even in the i8085 pre-release silicon.

    As to adding instructions, sure, if you're implementing the 8085 in an FPGA. Otherwise, no--they're hard-coded on the silicon. Tundra decided to document the added instructions, but their offering (CA80C85) is just a licensed clone of the Intel chip.

    I wondered (too late) why Intel declined to publicize the added instructions. One application engineer at Intel told me that it was done because the added instructions had no exact 8086 replacements--and they weren't on the 8080A, so they would be a dead-end. I guess I could understand.

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