C8051F060/1/2/3/4/5/6/7

C8051F060/1/2/3/4/5/6/7

23.2.2. 9-Bit UART

9-bit UART mode uses a total of eleven bits per data byte: a start bit, 8 data bits (LSB first), a programmable ninth data bit, and a stop bit. The state of the ninth transmit data bit is determined by the value in TB81

(SCON1.3), which is assigned by user software. It can be assigned the value of the parity flag (bit P in register PSW) for error detection, or used in multiprocessor communications. On receive, the ninth data bit goes into RB81 (SCON1.2) and the stop bit is ignored.

Data transmission begins when an instruction writes a data byte to the SBUF1 register. The TI1 Transmit

Interrupt Flag (SCON1.1) is set at the end of the transmission (the beginning of the stop-bit time). Data reception can begin any time after the REN1 Receive Enable bit (SCON1.4) is set to ‘1’. After the stop bit is received, the data byte will be loaded into the SBUF1 receive register if the following conditions are met:

(1) RI1 must be logic 0, and (2) if MCE1 is logic 1, the 9th bit must be logic 1 (when MCE1 is logic 0, the state of the ninth data bit is unimportant). If these conditions are met, the eight bits of data are stored in

SBUF1, the ninth bit is stored in RB81, and the RI1 flag is set to ‘1’. If the above conditions are not met,

SBUF1 and RB81 will not be loaded and the RI1 flag will not be set to ‘1’. A UART1 interrupt will occur if enabled when either TI1 or RI1 is set to ‘1’.

Figure 23.5. 9-Bit UART Timing Diagram

MARK

SPACE

BIT TIMES

START

BIT

BIT SAMPLING

D0 D1 D2 D3 D4 D5 D6 D7 D8

STOP

BIT

280 Rev. 1.2