Advanced Embedded Systems Design

1. Advanced Embedded Systems Design Lecture 8 Serial I/O BAE 5030 - 003 Fall 2004 Instructor: Marvin Stone Biosystems and Agricultural Engineering Oklahoma State University

2. Goals for Class Today • Questions over reading (Chapter 18, PC-Link) • Student presentation?? • Serial I/O • Demo Keil Compiler • Watch windows • Breakpoints • Code browser • Review Target Hardware • Circuitry / cabling • Demo • Set assignment

3. Serial I/O (RS 232) - Pont • History • Serial communications needed as an efficient low speed data exchange between data terminal devices (teletype) and data communications equipment (modems) • EIA (telephone industries) standardized the interface in the early 1960s (RS-232-C in 1969) and the CCITT (Comite Consultatif Internatinale de Telegraphie et Telephonie) later standardized V.24 (functional description) and V.28 (electrical specifications). • Application • Effective for low data rate communications (<10 kbaud) over short distances (<15 m) • Higher data rates may be used over short distances • Limited to Point-to-point applications • Few number of conductors required (minimum=3 for no handshaking duplex) • http://www.techtutorials.info/serial.html

4. Point to point Single receiver and single transmitter Direction Simplex – single direction Duplex – two directions Half duplex – one direction at a time Full duplex – both directions simultaneously Synchronous vs asynchronous Synchronous – bit stream is transmitted with a clock synchronised at both ends of communication Asychronous – Frames (characters) are sent as necessary without synchronization, bits are sent with an understood clock rate DCE = Data Communications Equipment eg. Modem DTE = Data Terminal Equipment eg. Computer Characteristics

5. Packet structure amd baud rate • Packet consists of: • Start bit (=1) • Data, 7 or 8, LSB first • May have a parity bit (Even, Odd, Mark or Space) • Stop bits, 1 or 2 (=0) • Baud rate • Baud – State changes per second • Common baud rates: • 300, 1200, 2400, 9600, 19,200, 38400, and 57,600 baud

6. Flow control • Hardware • RTS/CTS • Sender asserts Request to Send (RTS), Receiver asserts Clear to Send (CTS), Sender receives CTS and sends unless CTS is dropped. • Software • Xon/Xoff • Receiver signaled flow control through the data stream (needs full-duplex) • The Xon character [0x11 (decimal 17)] is sent by the receiver to signal the sender to send • The Xoff character [0x13 (decimal 19)] is send by the receiver to signal the sender to stop sending

7. RS 232 pin definitions • DTE (computer) device has a male connector (socket with pins) 9-Pin DB9-M male Connector on a DTE device (Looking into the connector)

8. RS 232 Voltage Levels • Signal logic • > +3v = 0 = space • < -3v = 1 = mark

9. USB – Universal serial bus • Next generation of serial I/O for PC to device • Bus oriented (127 devices) • Connector provides power • Uses enumeration to ID devices • High data rates • USB 1.1 - 12Mb/s or 1.5Mb/s • USB 2.0 - 480Mb/s • Isocronous communications capability – “music” • Excellent material on web • http://www.usb.org/developers/whitepapers/usb_20t.pdf • Development effort • Very significant effort to provide interface on embedded device. • Serial to USB devices attractive – use built in driver on host

10. Assignment • Assemble target hardware / cabling • Demo “Hello World” • Read Pont, Chapter 19,20,21,22 • Tutorial – 30 min • Review USB from a developers perspective