avsys:
thank you for the reply,
what is the meaning of "SJ"
you mean connection should be made to the 3.3v supply line?
SJ is a solder jumper so you can supply either 3.3v or 5v to pin 4 of the JP1 connector to power the device it's connected to (some Arduino's are 3.3v and others 5v).
Pin 4 of the FT232RL (named POWER) should be connected to pin 4 of JP1 (also called POWER)
If you look at the FT232RL datasheet you will see this pin is used to derive the UART voltage levels.
The user bridges the SJ2 solder joint to select 3.3V/5.0V voltage level supplied to the attached device and this voltage is also applied to pin 4 of the FT232RL chip (through a trace/wire called POWER in the schematic) so it knows what voltage to drive the CTR, DTR, TX & RX pins at.