Ooops!

I have just read back that message and I really did say it..... I am so embarrased now!

Erik is of course right; the outputs of the 8051 are open-drain with weak pull-up, so you can connect the TxD directly to the I/O line, without an external transistor (although an additional pull-up may be required).

As an excuse for my stupidity: I have been working almost exclusively with the Cygnal chips lately and their ports can be configured as push-pull. What's more, the Smartcard applications I have built had the TxD routed through a multiplexer, making it necessary to use an external transistor.

And now I think I' going to book a very long holiday......

Regards,
Rob.