Linux-Hams archive - July 1998: Re: Baycom problem - comment and question

Re: Baycom problem - comment and question

Duvall, Michael J. (iaxerkj@nokcolab.dk)
Wed, 1 Jul 1998 9:09:49 -0400

To get slightly off topic..

>It was not an arbitrary decision. Packets are a synchronous stream of
>8 bit bytes without stop and start bits. Serial ports are asynchronous
>only, there is no way to generate synchronous data using such a port in
>the normal way. The Baycom idea is just to use the control lines as
>convenient I/O bits. They are not controlled by the normal baud rate
>generation hardware, and there is no parallel to serial conversion in
the
>port. The timing is controlled by software and the CPU decodes the
stream
>of incoming data and generates the outgoing data stream. You must have a

>Baycom driver of some sort containing this software. Even if you change
>the connections you can't just connect a Baycom modem to a serial port
and
>receive and send packets that way.

Yuck!

Someone told me that the UART was used and as a result the Baycom
required little CPU time, just the normal UART interrupt overhead. I
guess my original fears were correct.

I think they call this a bit banger UART. Cheap and DIRTY! Unless CTS
generates and interrupt the CPU has to sit there a poll the port all the
time. In other words your expensive CPU and software are replacing a $5
part. This great for the back of a laptop computer. I don't know if I
would want to run more than one on a PC. I guess if it works go for it.

Mike Duvall
X2615