hi,
When RI is set, which is to say when the serial port interrupt is triggered, program control is automatically vectored to, I'm guessing 23H?

No, it does not "automatically vectored" as long as you have not serial interrupt enabled. So there are some ways to work with UART:
- utilize serial interrupt (write its ISR, enable both EA and ES, etc);
- work with RI and TI flags by polling them with serial interrupt routine disabled.

Regards,
Oleg