in reply to: HART preamble format posted by Anirudh on 23 November 2009 at 08:52:49.
HART uses asynchronous transmission, so yes, every character, including the FF preamble bytes, has the usual start, parity and stop bits. The start bit is 0 (2200Hz) and the stop bit is 1 (1200Hz). Parity is odd. The UART chip (or software function) should take care of all this - just send the FFs as the first characters of the message, before the start delimiter character.