Yes, Patrick is correct. The PC style UART can be setup to send data 5, 6, 7, or 8 bits wide. Then an optional parity bit can be appended. The RB8 bit in the target 8051 is a method whereby, then serial data stream is set for 8 bits wide that the target UART can receive the Parity bit. Likewise the TB8 bit is used to permit the 8051 UART to send a parity bit (although it need not actually be used as a parity bit when 8051's are communicating with other non-PC UART devices).

For the software of a PC to effectively control the bit value sent out in th8 9th bit position the prograammer can toggle the parity setting back and forth between MARK and SPACE. The Even and Odd settings of course determine the 9th bit from the content of the other 8.

Michael Karas