Re: Packet at the physical level

From: Richard Stearn (kecbc@mail.dy.fi)
Date: Fri Sep 19 2003 - 12:25:48 EEST

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    Mike Davies wrote:
    > Thanks for all the replies (so far). A little bit of fiddling here
    > has confirmed that valid packets can start with either tone. You learn
    > something every day.
    >
    > By the way, VHF amateur packet is not Bell202 compatible. I've
    > seen this mentioned before, but I've got the source code for a Bell202
    > modem which I know works, and that simply uses a 1300Hz tone for high bit
    > and a 2100Hz tone for a low bit. So not only does it use different tones
    > it doesn't do the NRZ modulation.
    >
    > Hopefully in the next day or two I'll be able to transmit a few
    > test packets, and then I'll be able to determine the CRC polynomial if
    > nothing turns up before.

    Mike

    The Z80-SIO-0's in my homebrewed 4-port sync serial card are set to:

            HDLC
            CRC16

    CRC16 is:
            x16+x15+x2+1
    the CRC generator is preset to 0's (non-HDLC)

    Info from Zilog comps databook 1983 and the source code for my 4-port sync
    serial card from about 1987 (still the mainstay of my packet system). 

    -- 
Regards
	Richard
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Amateur radio callsign: G1SOG         Home BBS: G1SOG@GB7GLO.#46.GBR.EU
                 Amprnet co-ordinator for Wiltshire
Unix is user friendly.        Just rather selective about it's friends.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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