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Thread: Compaq Portable 386: Serial port issues?

  1. #1
    Join Date
    Oct 2016
    Location
    Illinois, USA
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    285

    Default Compaq Portable 386: Serial port issues?

    So, I'm trying to get my desktop talking to my Compaq Portable 386 so I can transfer files. Problem is, nothing seems to be working - Fastlynx never makes contact, and Kermit makes contact but is unable to make any file exchanges (with packet length being incorrect on the receiving end). Kermit's also unable to make any contact if I enable handshaking or parity. So far as I can tell the port is jumpered correctly - anyone have any leads I can pursue? A serial mouse seems to work appropriately.

  2. #2

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    Test it with a loopback plug. CheckIt can do that.
    PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

  3. #3
    Join Date
    May 2006
    Location
    Melbourne, Australia
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    6,042

    Default

    If you are using a USB-to-serial adapter on your modern PC, then that could be the cause.

    I have two different types (different 'guts'), and neither works with FastLynx or LapLink. Others report similar. No problem if I swap to a motherboard based serial port.

    A related earlier thread is at [here].

  4. #4
    Join Date
    Oct 2016
    Location
    Illinois, USA
    Posts
    285

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    I am using a USB-to-serial adapter, in fact. Gonna have to try another machine, though at that point the ol' blank disc juggle from something my desktop can talk to would be about as fast. Weird considering it doesn't give me much in the way of issues with anything else I own - even talked to my NEC APC running Kermit86 with it without incident.

  5. #5

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    I'm speaking under correction, but some issues with USB Serial adapters may occur because they use different signaling levels than
    a conventional RS-232 port would use. As far as I remember, these adapters use TTL like levels like +5v and 0v, or more recently,
    +3.3v and 0v, whereas a V.24/RS-232 port would use 12v and -12v. For simple data transfer, that difference may not cause trouble,
    since the RS-232 is tolerant enough to recognize +5v as +12v and 0v as minus something.
    For old serial devices, however, like directly controlled transistor circuits (which do essentially use the datalines, rather than exchanging ASCII characters), they may not work properly. Except if the circuit in question works with low voltages also.
    (By nature, these USB serial adapters should support that bit-banging stuff like the real thing.)

    Another thing that may causes trouble is an outdated UART chip.
    The old 16450 has trouble with communciation programs, especially on higher speeds.
    Replacing it with a 16550A or higher pin compatible model could make connections more stable.
    Also, a 16550 doesn't cause interrupts as often or so I heard. This could improve performance in some cases (Win 3.1 ?)
    "Time, it seems, doesn't flow. For some it's fast, for some it's slow.
    In what to one race is no time at all, another race can rise and fall..." -The Minstrel

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