Texas Instruments MSC1210 - Manual (Page 97)

Setting the Serial Port Mode
9-7
Serial Communication
Figure 9−3. Serial Port Mode 1 Transmit Timing.
Figure 9−4. Serial Port 0 Mode 1 Receive Timing.
Reception is enabled by configuring SCON0.RBN = 1. Reception of the data
begins at the falling edge of start-bit detection. The RXDx pin is sampled 16
times-per-bit for any baud rate setting. When the falling edge of the start bit is
detected, the divide-by-16 counter used to generate the receive clock is reset
to align the counter rollover with the bit boundaries. The state of each bit is de-
termined by a majority detect decision on three consecutive samples in the
middle of the bit; this provides an amount of noise rejection. At the middle of
the stop-bit time, the serial port verifies that the status of SCONx.RI_x = 0 and
SCON0.SM2_x = 1 (if SCON0.SM2_x = 0, the stop bit is a don’t care). If these
conditions are true, then the serial port writes the received byte to the SBUFx
register, loads the stop bit into SCONx.RB8_x, and sets the SCONx.RI_x flag.
If the conditions are not met, the data are ignored. After the middle of the stop
bit, the serial port waits for another start-bit detection.