[NTLUG:Discuss] Reading raw serial input?

[Steve Baker]

Elequin wrote:
> 
> I'm new to anything involving serial ports or parallel ports in linux,
> so please forgive the newbie question.  (Hell, it took me an hour to
> figure out what device to use in minicom to connect serial to my cisco!)
> Anyway, I have this cute little device called a Sohotools Connect-ID
> that basically listens on the phone line and collects caller-ID
> information, and then reports it to a piece of Windows software via
> serial port.  I hooked it up via serial to one of my linux boxes and
> opened up minicom and then placed a call to my home phone.  All it did
> was spit out a bunch of garbage.  It apparently reports name and number
> info, plus maybe a timestamp.

Well, if you are seeing garbage in Minicom, you probably just have the
wrong baud rate.  If you don't know what rate this Connect-ID box uses,
that's a very likely possibility - you'll have to cycle through all of
them to find out what it's using.  I'd start at 9600 baud and work up...
but telephony signalling rates are quite low - so maybe this box works
at a much lower baud rate.

Another possibility is that it has a parity-check bit on each character.
you can configure Minicom to enable either odd-parity, even-parity or
no-parity.  The default is likely to be 'N81' mode (No parity, 8 data bits,
1 stop bit), perhaps you need 'E71' or 'O71'.  If the box is sending data
with parity and you view it with parity turned off then about half of the
characters would come through looking OK and the other half would be garbage.

Yet another possibility (a MUCH nastier one) is that it may not send the
data in ASCII.  It might be sending the phone number as a binary integer
in the first few bytes then the timestamp as some binary number and the
letters of the name as 0==A, 1==B or something.  That's pretty unlikely,
but it's certainly possible.

>  Are there any utils available to read raw serial port input?

Not as such - but you don't need any special utility.

One of UNIX's more powerful concepts is that "Everything is a file".

The serial port is nothing special in UNIX/Linux: /dev/ttyS0 and /dev/ttyS1
look just like infinitely large files to most applications.  If you have
the right baud rate, etc, then you should be able to display what's coming
from the serial port just by writing:

   cat /dev/ttyS0

...although you may have to use the 'stty' program to set the right parameters
to the port and you may need to be 'root' or at least to 'chmod a+rw /dev/ttyS0'
to give yourself access privilages to that port.

You can then do things like:

  cat --show-nonprinting /dev/ttyS0

...which will show those garbage characters as ^X and so on so you know what
they are.

However, I would continue playing with Minicom, tweaking the settings until
you see good data before going on to this next step.  Minicom is much more
friendly to the novice than 'stty' when it comes to playing with serial port
parameters.

----------------------------- Steve Baker -------------------------------
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