1. Spring 2007 1 EE 316 Computer Engineering Junior Lab Serial Ports

2. Spring 2007 2 PC's Serial Ports ● PC's Serial port (RS-232c interface) is also known as the communication (COM)port. ● The serial port transmits a byte of data by sending 8 bits separately. It adds a start bit, a stop bit and if desired, a parity bit. ● COM ports are bi-directional. Serial ports use a special controller chip known as the Universal Asynchronous Receiver/Transmitter (UART), to function correctly. ● Used to connect to Modems, some printers and digital cameras. Ref: http://computer.howstuffworks.com/serial-port.htmhttp://computer.howstuffworks.com/serial-port.htm

3. Spring 2007 3 PC's Serial Port, contd. ● Serial cables can be longer than parallel cables. ● The RS-232c data uses -3 to -12 V to represent a 1 (called Mark) and +3 to +12 to represent a Logical '0' (called Space). ● Serial data must be converted to TTL/CMOS level for digital circuits. http://www.beyondlogic.org/serial/serial1.htm#40

4. Spring 2007 4 PC's Serial Port, contd. ● One can use the RS-232 drivers and recievers to transform the RS-232 level to TTL/CMOS level. http://www.beyondlogic.org/serial/serial1.htm#40

5. Spring 2007 5 UARTs Universal Asynchronous Receiver/Transmitter ➔ To use the serial data in digital applications, we need to convert the TTL/CMOS serial data into parallel data using UARTs. ➔ Popular UARTs: 16550, 16450 & 8250 series ➔ We will use a CMOS based UART: HD- 6402. Read the data sheet carefully before using. ➔ UARTs use a clock with is 16 times the baud rate of the serial port.

6. Spring 2007 6 UART Timing & Control Issues

7. Spring 2007 7 Interfacing a digital system with a PC (another digital system) PC and its UART and level converter MAXIM 233UART

8. Spring 2007 8 References  http://computer.howstuffworks.com/serial-port.htm http://computer.howstuffworks.com/serial-port.htm  http://www.beyondlogic.org/serial/serial1.htm#40 http://www.beyondlogic.org/serial/serial1.htm#40