SPRUJ53B April 2024 – September 2024 TMS320F28P550SJ , TMS320F28P559SJ-Q1
The SCI asynchronous communication format uses either single line (one way) or two line (two way) communications. In this mode, the frame consists of a start bit, one to eight data bits, an optional even/odd parity bit, and one or two stop bits (shown in Figure 23-7). There are eight SCICLK periods per data bit.
The receiver begins operation on receipt of a valid start bit. A valid start bit is identified by four consecutive internal SCICLK periods of zero bits as shown in Figure 23-7. If any bit is not zero, then the processor starts over and begins looking for another start bit.
For the bits following the start bit, the processor determines the bit value by making three samples in the middle of the bits. These samples occur on the fourth, fifth, and sixth SCICLK periods, and bit-value determination is on a majority (two out of three) basis. Figure 23-7 illustrates the asynchronous communication format for this with a start bit showing where a majority vote is taken.
Since the receiver synchronizes to frames, the external transmitting and receiving devices do not use a synchronized serial clock. The clock can be generated locally.