Texas Instruments MSC1210 - Manual (Page 101)

Setting the Serial Port Mode
9-11
Serial Communication
9.2.4 Serial Mode 3: Asynchronous Full-Duplex
In mode 3, serial data transfers are 11 bits, full-duplex, and asynchronous. Mode
3 is identical to mode 2, with the exception of the baud rate. The transfer begins
with a start bit, followed by eight bits of data (LSB first), an additional bit of data
(ninth bit), and then a stop bit. On transmit, the ninth data bit is set by TB8. On
receive, the ninth bit is shifted into the RB8 bit in the SCON register and the stop
bit ignored. The baud rate is set by Timer 1 (USART0 or 1) or Timer 2 (USART0).
RXD is used for receiving data, TXD is used for transmitting data, LSB first.
On transmission, SCON.TB8 is used for the ninth bit. On reception, the ninth
bit goes into RB8 in the SCON register. The baud rate is adjustable and is
based on either Timer 1 or Timer 2.
Transmission is initiated by any instruction that writes to SBUF. The transmis-
sion begins after the first rollover of the divide-by-16 counter after the write.
The SCONx.Ti_x interrupt flag is set when the stop bit has been placed on the
TXDx pin.
Figure 9−7. Serial Port 0 Mode 3 Transmit Timing.
Figure 9−8. Serial Port 0 Mode 3 Receive Timing.