[amsat-bb] Re: FX614
n2por at amsat.org
Fri Jul 24 23:56:46 PDT 2009
On Fri, 24 Jul 2009 13:50:35 +0200
Andy Brian <briaandy at gmail.com> wrote:
> I'm looking for any simple source code in C-language for FX-614 (ax.25
> decoder) for undestanding simple ax.25 protocol.
I'm would also like to find a C implementation of the ax.25 protocol. The only one I know of is in
linux kernel (in net/ax25). I'm not sure if that is that simple because it may have too many kernel'isms in it.
But first some background info:
When dealing with 1200 baud ax25 things built on things:
hdlc (takes the bits and makes it a package frame)
bell 202 (tones for the bits)
Now since the packets are sent over the air as sync and not async (the whole packet is one continuous string of bits) you can't use the async clock recovery stuff in the chip. Also because of this you can't use the transmit and receive data pins on your standard async serial port.
Back in the DOS days, baycom came out with a modem similar to what your talking about (and there were several clones using tcm3105 modem chip). It worked by sampling one of the other leads on the serial port fast enough to do clock recovery and hdlc decoding. (there were also ones that tied to the parallel port)
(search for baycom and/or tcm3105)
You didn't mention what operating system your running on your pc.
It looks like there are still baycom drivers in the linux kernel (source drivers/net/hamradio, some docs somewhere in the Documentation directory) Don't know what the status is.
(I haven't dealt with this, but I have done other ax25 things with linux in the past)
dos: search the web
windows: I don't have a clue. I don't even know if it's possible without a kernel level driver.
after you have the clock recovered, the hdlc frame decoded, and checksumed, handing the packets off using kiss or 6pack or doing things using unconnected packets either point to point or multicast like aprs or as a base of a pacsat downlink protocol is just rearanging the bits.
full duplex transmit is just bit twiddling and then sending them out at the right rate.
half duplex there are several timers to worry about so you don't collide with other people.
ax.25 can get complicated with other things
> I found only few
> asm code for PIC16, but c-lanugage is easily to adopt to other microcontrollers.
> I tried to connect FX614 IC like in HITSAT
> http://www.hit.ac.jp/~satori/hitsat/img/decord.bmp and read at RX PC
> port with rs232 terminal programme,
> but I didn't receive any useful frame with b011111110 start (like
> describet in ). After this I found that all modem using pin CTS on
> RS232 port, I don't know how to handle this with
> PC to read directy with rs232 RXD port like HEX or binary values to
> see raw values of packet frames?
> It is possible to read values from FX614 (through max232 ) with PC to
> see raw format?
> So I'm looking for any simple source code in C to find how to decode
> signal from fx614 to microcontrollers port and then to PC
> Thanks for your help
> all the best Andy
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