USB-TTL Serial Bridge with CP2102 chip it's for 2,3€ (included shipping) available on ebay.com so it's really cheap. http://www.etheus.net/CP210x_Linux_Driver http://www.silabs.com/products/mcu/Pages/USBtoUARTBridgeVCPDrivers.aspx
It has needed pins Gnd, RxD and TxD, and also all other featured RS232 Pins, but not needed. and 5V and 3,3V outputs
Tested and working properly with OpenSuse12.1, driver under Linux Kernel 3.1 included, no problems using it with minicom. Also working with MS Win Vista without problems and putty.
First you need to find the CON401
Pin 1 = GND
Pin 3 = RxD
Pin 6 = TxD
Solder three wires on the CON401 as described. An old PATA cable is useful as seen on this pictures
Take a file and make a little hole at the place where to put the cable through. Mark the Ground Cable, at the picture it is marked with pink colour.
After that connect
Gnd with Gnd
RxD with RxD and TxD with TxD,
because on the converter it is wrong printed.
Otherwise, if you don't get the connection established, cross the RxD and TxD wires. RxD→TxD and TxD→RxD
Open up a serial connection with HyperTerminal or Putty in windows or minicom, cutecom, putty etc in linux. Serial connection parameters: 115200 8N1 (8N1 == 8-bits per character, no parity, and 1 stop bit)
When booting hit CTRL+C == ^C to stop RedBoot running the Boot Script and Redboots starts with