Matrix Orbital Corp

I've got a GLK-12232-25-WBL, PCB revision 2.0, connected to a serial port using the Matrix Orbital-supplied communications cables. (I've actually got both http://www.matrixorbital.com/product_in ... ower-cable and http://www.matrixorbital.com/product_in ... -cable-4br, and see the same behavior with both.) Power is supplied from a floppy drive pigtail; yes it's connected properly and always has been.

With only the power connector connected, the display seems to work fine-- the backlight lights up, the screen displays the "Graphics in any Direction" logo, and it seems bright and clear. The moment I connect the DB9 connector on the communications cable to a serial port, the display goes blank and the backlight shuts off. If I disconnect the cable from the serial port, the display and backlight return (still displaying the boot logo.) I don't think I'm successfully communicating with the board when the cable is connected; characters echoed to the serial port (at 19200 8N1; checked that about a million times) don't show up on the display, and commands like 254 55 (read module type) don't provide any response. It's as though the unit is not powered at all when the serial connection is made.

I inspected the connection with an inline RS-232 tester. With the tester connected to the GLK but the GLK not connected to a serial port, TD is the only pin pulled low and the display is on. When I connect the other end of the tester to the serial port, I see the expected sender-side activity but lose the display. I don't ever see any action on the clear-to-send or carrier detect lines, though, furthering my suspicion that the GLK is not responding to serial input at all.

Is there anything else I should check? Is the hardware simply defective? Is it possibly a problem with my serial port settings or cabling? Both the port and cable seem to work fine with other devices, although I realize that's not exactly conclusive.

Thanks for any help...

OK, I guess the first post was a bit premature--- after a little more fiddling I've found cabling arrangements such that instead of the display going blank when it is connected to the serial port, the background gets stippled with dots (not in a regular patter, though), so that it appears darker. The Graphics in any Direction logo remains on screen and is still legible, although somewhat less so due to the stippled background. When I disconnect the serial port the background clears up again. The module still doesn't respond to commands sent over the port, unfortunately.

Hi spillner,

I wonder if you could please try something out for me. On your communication and power cable, please swap the two middle pins, I believe they are white and green wires. Place the white wire to where the green is, and the green to where the white is.

I believe, if you can read on the PCB, that the connections on the power connector are: GND, RX, TX and 5V. The communication and power cable I believe is connected to be: GND, TX, RX and 5V.

Please let me know how it turns out.

Best Regards,

Raquel,

I didn't rewire the cable, but I found that inserting a null modem (for the same effect) clears up the "random dots" effect. Thanks for your help!