This is a how-to as to the installation of a working serial port on the Matrix TBS2910. Do this on your own risk although I don't think that you can brick anything easely.
What do you need:
A RS232-TTL convertor, bought from Ebay <2$.
An old cable that used inside a PC to connect the CD player with the audioheader on a motherboard. This cable fits to the Matrix on one side and the other side fits to the convertor. The connectors can be disassembled by carefully lifting the plastic tongues somewhat en then pulling out the metal part. In this way you can simply change the wiring on the connectors. Best us to do this on the black one, this is bigger and easyer.
The pin-out of the matrix UART starting from left:
VCC (black wire)
Rx (red wire) connects to Rx on the convertor
Tx (black wire) connects to Tx on the convertor
Gnd (white wire)
On the pcb of the convertor the pins are indicated. I removed the screws and the metal housing on the RS232 connector, now you can simply plug it into your PC. To test, install Putty on your PC. With this programm you can make an serial connection on COM1 (the serial port on your PC, or COM2) with speed 115200. When you boot the matrix you can see messages apear on the screen of the terminal.
Warning: When you use a serial cable between your PC and the convertor this might not work because I believe that RX on one side is connected to TX on the other side of the cable. In this case you can swap the RX an Tx wires on one connector.
Remember: The UART is configured as a console for debugging. When you want to use it as a serial port for other purposes then the boot cmdline has to be altered. Google for "serial port on raspberry PI" for further information about this. But on the Matrix I think you have to do this in the u-boot. I did't try this yet.
foto's: wireing   RS232-TTL convertor   RS232-TTL convertor
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