[aprssig] RE: WRT54G - now simple embedded computer

Dave Baxter dave at emv.co.uk
Fri Nov 23 04:07:38 EST 2007

Buffered ports are not the answer, you still need to service the buffers
in reasonable time.   If you don't and you don't tell the external
source the buffer is full, you will still lose data.

It's not a hardware issue, it's a programming issue.  If you stick to
using an interpreted language like Basic on a microcontroler, even with
the 32MHz part, you may still have problems handling more than one data
stream at a time if you have to emulate the serial devices, even it the
code works without tripping up, the bit timing could be a little

If you can get into it with assembly language (or maybe C) and
interupts, even with the 4MHz part, two serial data streams running
concurrently should not be a problem.  But doing it relaibly will take
some skill in the software design.  (I used to do all that with a 4MHz
Z-80 in years gone by at 4800bd)

For a device to "translate" one serial protocol to another, perhaps use
a chip with at least one built in serial device, and do the second one
in software if needed.


Dave G0WBX

> -----Original Message-----
> From: Greg D. [mailto:ko6th_greg at hotmail.com] 
> Sent: Thursday, November 22, 2007 4:14 AM
> To: TAPR APRS Mailing List
> Subject: RE: [aprssig] RE: WRT54G - now simple embedded computer
> Hi Bill,
> You need something with real (buffered) serial ports on it.
> I believe any pin on a Stamp can be used for a serial port - 
> look at the SERIN command.  The main problem you will 
> probably run into is that the Stamp only does one thing at a 
> time.  If it's sucking in bits from one port, then it's not 
> looking at the other one.  So after reading a character from 
> one pin, you will miss the next one while you are pushing the 
> first one out the second port.  
> Does Parallax have anything with "real" ports on it?  
> Otherwise you might consider picking up an old X86 PC.  
> Probably cost a lot less than a Stamp, anyway.
> Greg  KO6TH
> ----------------------------------------
> > Date: Tue, 20 Nov 2007 17:18:48 +0000
> > From: wa7nwp at gmail.com
> > To: aprssig at lists.tapr.org
> > Subject: [aprssig] RE: WRT54G - now simple embedded computer
> > 
> > I've been searching for months for a simple embedded system that
> > simply has two real serial ports.    Effectively all I want is to
> > connect a standard landline modem to a standard external 
> > TNC.  I just 
> > need the computer to handle the handshaking and issue a couple modem
> > ATxyz strings.   After that it would simply pass the bytes back and
> > forth.  Any suggestions?   The Basic stamps are close but I haven't
> > found one with two serial ports.
> > 
> > Thanks,
> > Bill - WA7NWP
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