Serial Wombat
a general-purpose digital interface device for hobbyists, engineers and students

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Interfacing the Serial Wombat via Ethernet Using a Lantronix XPort for TCP/IP-to-RS232 conversion

I finally got around to hooking up the Lantronix XPort I've had sitting around for a couple of months. Basically, the XPort seems to be a little embedded server all housed in a small package which includes an ethernet jack. You can pick one of these guys up at Mouser for a little over $50. I guess the XPort is designed for you to code and install your own Web Server software, but they ship it pre-programmed with a program that does Telnet to Serial conversion, which is good enough for me.

The XPort was easy to use. I soldered wires on to the first 5 pins on the bottom (Ground, +3.3 v, Reset, TX and RX). There's three more pins I didn't use. These can be used for flow control (not currently supported by the Wombat), or GPIO. It appears that you can manipulate the GPIO pins from the ethernet interface. This might be super useful for tying to the Wombat's reset pin, so that it could be hard-reset from a distance. I'll try this in the future.

The XPort requires a 3.3V power supply. I used a TC1262 from Microchip, fed from the 5v output of the 7805 feeding the Wombat. The Xport is tolerant of 5v input, so you just tie the TX and RX pins from the XPort directly to the RX and TX pins on the Wombat.

You can set up the IP address for the XPort using a software utility for Windows from Lantronix. Mine worked good, and detected the XPort on the first try. I configured it to work on my local 192.168.XXX.XXX subnet.

Once this is set up, you can Telnet to port 10001, and it bridges the ethernet connection with the Serial I/O of the XPort. By default this is at 9600 baud. I had to go through the documentation a couple of times before I realized I wasn't supposed to telnet to port 23.

The only problem I had was that the XPort didn't seem to like the sloppy powerups provided by attaching and detaching a 12V battery from my 7805. When I do a real application using the XPort, I'll probably tie its reset pin to a Wombat pin, and hold that pin low for a second or two at powerup, using the Wombat's ability to manipulate pins from EEPROM commands at Powerup. The XPort docs say it has its own 200ms powerup circuit, but I had trouble with lockups at powerup. Reset pin always fixed this.

The XPort documentation seems to be written by software people for software people. I couldn't find anywhere in the docs how much current the XPort pulls, and other electrical statistics common to electronic components are also not in the docs I found. The docs do recommend providing a ground plane for cooling the package on your PCB, but I didn't do this since I'm using a breadboard. After about 20 minutes of operation, the case was only warm to the touch.