This question asks about endian issues of the S-100 bus. A peripheral card that has a register larger than one byte (e.g. a 16-bit or larger word) would need to be read/written by more than one access; endianness then becomes an issue.

Did any peripheral cards for the S-100 bus have registers larger than one byte?

To be clear, I am asking about actual products, not whether it was theoretically possible.

  • 2
    IEEE Std 696-1983, a master could assert sXTRQ* and a slave could assert SIXTN* for 16-bit transfers. See 2.6 8/16-bit Data Transfer Protocol.
    – user9041
    Nov 15, 2020 at 3:43

1 Answer 1


I have never seen any 16 bit I/O cards. There wasn't much business sense to build such, as it would have quite limited possible sales.

(CPU)-Boards according to the IEEE standard for 16 bit access (*1) had to be able to turn any 16 bit request into two consecutive cycles to enable seamless interaction with 8 bit boards. Making a card requiring single cycle 16 bit access would have limited the use to 16 bit CPUs only.

But there have been several memory cards, like this 256 KiB static or this 1 MiB dynamic RAM, that could be configured to for 16 bit transfers using the IEEE 16 bit extension (*1).

In general 16 bit RAM boards are a rather rare find. Usually 16 bit CPU CPUs did bring plenty on-board memory and/or proprietary interfaces (*2), as S100 bus speed was usually limited to 4-6 MHz, considerably slowing down operation.

*1 - See this answer for details.

*2 - Same is true for Multibus boards - but here more to avoid bus arbitrating.

  • 1
    Just to be clear: The question is not about boards that used the 16-bit data bus. Nor is it about RAM; you are correct in your answer to the other question that RAM doesn't care about endianness. The question is about peripheral registers that are larger than a byte, such as might be used by a 16-bit timer or counter.
    – DrSheldon
    Nov 16, 2020 at 2:26
  • @DrSheldon I believe the first two paragraphs do answer your question. 16 bit IO which relies on single cycle access does not make much sense. They are not only a solution without a problem, but as well hampering potential sales. Card manufacturers usually care to sell to as many users as possible. The part about memory has been added to make it whole, showing that even 16 Bit RAM, which is least problematic, didn't make big sales.
    – Raffzahn
    Nov 16, 2020 at 3:05
  • 2
    I guess in "like described in." you forgot to put in the link you wanted to put in?
    – dirkt
    Nov 16, 2020 at 5:31

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