06/06/88: TELECOM programs by Delphi, | Category: Delphi - Telecommunications | 11 comments - (Comments are closed)

TELECOM programs

41714 6JUN88-0045 Telecommunications
TELECOM programs

I’m currenly working on a terminal program. If all goes well, I’ll post it
here in DELPHI. I think I understand parity bits, but I’m not sure how to
handle incorrect bytes sent from the other computer. Should I send a NAK
character? Ignore it all together causing it not to echo to the other computer?
Or what. And with XMODEM, I assume that I don’t echo any of the chr$ except
the checksum, right? Or do I just send a ACK chr. I quess I don’t understand
it as well as I thought. Any help will be appreciated.
Ken Halter

11 comments to TELECOM programs

  • pucc_unknown

    41787 9JUN88-0042 Telecommunications
    RE: TELECOM programs (Re: Msg 41714)

    During normal communications, there’s really not much you can do about
    receiving characters with the wrong parity. Some terminals display
    such “munged” characters as question marks. Most terminals and
    communications software just ignores parity, and strips it off
    just prior to displaying it. Thus if you get some “garbage” characters,
    they appear as obviously wrong characters displayed amongst perfectly
    normal looking text.

    Don’t bother to ACK or NAK them, just display them. If you NAK a
    parity error, chances are virtually certain that the computer
    won’t know what you’re talking about.

    I believe we have a file in the databases here, uploaded by MIKEWARD,
    that explains the XMODEM protocol. That would make informative
    reading, judging from your other question. On an XMODEM receive,
    you really do not echo ANYTHING to the screen; you just stuff the
    data portion of each block into the buffer and/or the disk file.
    Each block is preceded by a header that gives some info from which you
    can validate the block, and also has a checksum at the end
    that serves the same purpose. If everything checks out, you can
    keep the yummy data that is “sandwitched” between the data header
    and the checksum. In that case, you send an ACK to the computer,
    to tell it, “That was great, now send more”.

    In the case of an error, of course, you send a NAK to tell the
    computer “Whoops, that don’t look too good; better send that again.”

    There’s more that’s involved, but that’s a quick summary. Take a
    look at Mike’s file for the whole scoop.

  • pucc_unknown

    41820 9JUN88-2336 Telecommunications
    RE: TELECOM programs (Re: Msg 41787)

    Thanks for the help Rick. Since I already have your attention, I assume
    that you’re the same Rick Adams that wrote the game SHANGHI. If so, I was
    wondering if you could give me a hint as to how to patch that game for
    monochrome output. It’s really hard to see with the color burst signal
    enabled. Do you think I might be better off buying a monochrome output for
    my COCO3, like DISTOs. Again, any help is appreciated.
    Thankyou, Ken Halter