[GreenKeys] USB -> RS232 update

[gil smith]

Hi Bill:

At 07:57 AM 4/19/2006, you wrote:

>(snip)
>3.  Long term, we'll probably need to go down the path Gil hinted out
>earlier - ethernet to RS-232/loop.  I'm currently using a commercial gadget
>that does this for another project of mine, the Lantronix UDS-200 device
>server - and it is a nice, slick solution.  However, the devices in this
>class that I'm aware of won't support our odd baud rates.  However, there
>are a lot of microcontroller solutions out there that come with ethernet
>support (such as the Rabbit family), so a custom teletype solution shouldn't
>be too much of a problem.

Well, if HeavyMetal just talks ascii at 38400, then you can use my 
TTY-Connect box to drive any machine, at any speed.  I have already done 
the ascii/baudot conversion and speed conversion.  It uses the pc serial 
port's xon/xoff flow control to throttle the data transfer from the 
pc.  Quite simple and works quite well.

I am familiar with the Lantronix UDS converters.  The ethernet option I was 
mentioning is actually a Lantronix XPort module, an entire 
ethernet-to-serial conversion system built into the 8P8C can.  It's pretty 
cool, and we are using them in quantity for a work project right now.  In 
single quantities from Mouser, they are only about $50!

They take 3.3V at about 300-mA, and provide 3.3V logic-level serial 
i/o.  Since my stuff is all 5V, that was a problem.  You can drive the send 
line with a 5V signal, but they have no open-drain/pullup option for the 
receive line.  However, putting an HCT gate (not HC) between them provides 
the proper level step-up.

To use them, your pc app needs to connect a tcp socket to the unit's ip 
address, and then just send and receive data, just like the UDS units.  You 
can make the address static, or just let it use DHCP to get an address 
assigned from the router.  Finding the dynamic address is still a problem 
but there is some discovery mechanism available (I have not looked into 
that yet).

I don't know whether you can do 5-bit 45-baud stuff with it or not, but I 
was toying with putting one into TTY-Connect.  Problem is, then I would 
need to buffer data.  With a simple serial port, the pc's internal buffer 
does all that for me now.  The xon/xoff flow control chars will still be 
sent over the socket connection, but now the pc application has to handle 
it, whereas in a serial port design flow control is handled by the driver 
and is transparent to the app.

fwiw,

gil




>...Bill Buzbee
>http://www.buzbee.net/heavymetal



Vaux Electronics, Inc.
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