Thank you very much
It is most likely the limited processing power of the AT device that restricts the throughput to 4800bps.
It you want something far more flexible you need to look at something like the FTDI or Silicon Labs CP210x series, which are also available in small packages if you are space constrained.
I'm sticky to attiny45 cause the size.
Any information on how to modified it to get "standard" 9600 bps?
FTDI chip very hard to get part in my country.(must be on-line puchased)
Any possibility to get standard serial "9600 bps"? How's about added crystal oscillator like:http://www.harbaum.org/till/i2c_tiny_usb/index.shtml
perhaps fixed baud rate at rate 9600bps??