From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Stearn Subject: Re: Packet at the physical level Date: Fri, 19 Sep 2003 10:25:48 +0100 Sender: linux-hams-owner@vger.kernel.org Message-ID: <3F6ACB9C.7020008@rns-stearn.demon.co.uk> References: Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: linux-hams@vger.kernel.org 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. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~