Serial links are a widely used, simple and cheap means of communication, where bytes are transmitted as a sequence of bits one by one. The data format is shown in Figure 118.
When data is not being sent, the serial link is said to be idle and is high (1 or mark). To indicate the commencement of the transmission of a byte (8 bits) of data, a start bit is sent (0 or space) for one baud period (the baud rate indicates the bit rate here). The 8 data bits then follow for the next 8 baud periods. (The byte often consists of 7 data bits with the eighth bit being a parity bit for error correction.) The transmission is terminated by a 1 for one baud period. After this, other bytes can be sent in turn.
The 5206 has two universal asynchronous receiver transmitters UARTs for serial communications on-chip, Figure 119. Further, the SBC main board has additional UARTs (one of which we use for communication with the host PC).
The UARTs can be configured for a number of standard serial communication arrangements, one of which is full duplex, Figure 120. This uses the RxD and TxD pins, plus ground.
Other arrangements may make use of the flow control pins CTS, RTS.
A detailed discussion of serial communications is given in Clements, Chapter 9. In particular, the widely used RS-232 serial standard is described, as are two common serial interface chips, the 6850 UART and the 68681 DUART.
An appendix to HLAB9 describes how to set up a simple one-way serial link. An assembly program txs.s is given which configures UART1 to send a byte in register D7 through pin txd1.
Detailed documentation on the 5206 UARTs is provided in Section 11 of the Motorola MCF5206 User Manual.
ANU Engineering - ENGN3213