I'm working on an app that uses the UART for RS422 data transmission -- which means that I need to turn on the level shifting device outputs just prior to the first message byte going out and turn off the level shifting outputs just after the last message byte going out.

It seems to me that the the normal simple 8051/8052 parts have an unbuffered transmit which tells me that the TI flag is set after the byte has been transmitted (the Tx data register is empty). From that I am concluding that I can disable the Tx level shifting outputs on the next interrupt following my last message char (transmit complete). Does this seem to hold for most of the common (non-turbo or otherwise enhanced) parts?

Am I reading this correctly or is, in fact, the Tx buffered and the interrupt only indicating that the data has been transferred from the holding register to the shift register (in which case I'm screwed)?

Thanks!