[Xastir] Suggestions and questions

[Henk de Groot]

At 11:16 9-6-03 +0200, Christian F1GWR wrote:
>2 I own a Baycom KISS modem, tied to a (perfectly working) Keyspan USA28X 
>USB-serial converter.  With the ZTerm application, an oscilloscope shows 
>that Start-stop signals are present on DB9 pin 3. The thing is Baycom 
>doesn't use pin 2 & 3 but DTR 4 (20) FOR TxD, CTS 8 (5) for RxD, and RTS 7 
>(4) for PTT. Is this modem Xastir (serial KISS TNC option) compatible? 
>Beside that, am I to install AX-25 layer?

This is not a KISS modem but just a BayCom modem. A BayCom modem is just a 
modem chip and some very simple interface electronics. It is conencted to 
the serial port but does not realy make use of the serial port 
capabilities, you can also connect it to the LPT port! The COM port makes 
asynchroneous serial data but on air synchronous serial data is used, so 
the serial port data can't be used as is. So instread the BayCom group just 
used the serial port in an unusual way. The serial port TX line is used to 
power the modem and the CPU constantly monitors the CTS line to read the 
serial data. For 1200 baud the CPU reads the CTS line 3600 times per second 
so every bit is sampled 3 times. By watching the bit changes the PC can 
stay synchroneous with the data and decode it. For transmission the PC just 
puts the data on DTR, this requires a stready 1200 Hz interrupt.

There are hard timing constraints and to meet those direct access to 
hardware, interrupts and PC timers are needed. On the PC this works in DOS, 
with a special AGW driver in Windows and with a specialized driver in the 
Linux kernel. On a MAC I think you are lost, I'm not aware of any 
implementation for BayCom style modems on a MAC.

The best is to use a real KISS TNC. A good alternative may be John Hanson's 
(W2FS) KISS modem which appeared in QST of November 2000.

At the end of thr article it says:

"A complete kit of parts including the PC Board, a programmed PIC 16F877 
and all other parts (except an enclosure) are available for $65 from John 
Hansen, W2FS, 49 Maple Ave, Fredonia, NY 14063."

I think with Google you can find more references and information.

Kind regards,

Henk.