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Thread: Question about 3270 Coax Protocols

  1. #1

    Default Question about 3270 Coax Protocols

    Hi all,
    I've been trying to learn about the protocol IBM used between their coax terminals and the controller such as the 3174. I've found some documentation on the Type B terminals like the 3277, but I'm more interested in the Type A implementation, used for the 3278/3279. I'm not looking for a detailed explanation of the 3270 protocol since I know it can fill multiple books, but rather just hoping someone can point me in the right direction.
    Pretty much everything I know at the moment comes from the CHIPS 82C570 data sheet. Given the amount of ISA emulation boards and clone terminals made I would think this information must be out there somewhere.

  2. #2


    There is a wealth of information in this directory:

    This document gives a good, basic and concise description of the basic 3270 protocol over coax, including the electrical and timing specs and the basic 13-bit 3270 frame:

  3. #3


    Thanks for the links, although from what I've gathered the documents there only describe the connection to a 3277 terminal, which is of Type B (or is it Category B).

    Well, my other option is to get a 3174 running, but as people have pointed out the microcode is hard to find and harder to duplicate. But I was wondering if it would be easier to image and emulate the 20mb fixed disk drive. It appears to be a ST506/412 drive in a specialized caddy. Has anyone tried this?


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