Thank all for help.
Thank Peter for good idea with using parity bit. I should check it necessary.

Question to Bruno:
I use AsincPro3 with RS485 mode support.
I read in documentation:

"When RS485Mode is set to True all PutXxx methods raise RTS before transmitting the first byte, wait for the data to be completely transmitted, then lower RTS."

This is not right!

Really:
raise RTS before transmitting the first byte, then through 200 mks (for 9600 speed) lower RTS and only then transmitting data.
This different between NT and 98 or more problems?

I'd like to use AsincPro and 8 bits data packet frame with address device in first byte.
However, I should check 9 bits mode on side controller and 8 bits with parity bit mode on side PC.
Maybe this more good way probably.

Thanks.