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Serial Communication Part-16
The document provides an overview of serial communication, specifically focusing on Universal Asynchronous Receiver Transmitter (UART) and RS232 protocols. It explains the concepts of asynchronous versus synchronous transmission, bit periods, and baud rates, detailing the structure of data frames used in UART communication. Additionally, it discusses the setup of AVR UART, including the configuration of the baud rate and data bits.
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Serial Communication Part-16
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- 3. www.techvilla.org.in Basics of serialcommunication Serial versus Parallel Data Transfer
- 4. www.techvilla.org.in UART • RS232 standardand application, e.g. 4 3 RS232 port (UART) RS232 port (UART) RS232 standard 3 wires +10 V=‘0’=SPACE -10V=‘1’=MARK Pin2 Pin3 pin5 Pin3 Pin2 pin5
- 5. www.techvilla.org.in U Universal AAsynchronous R Receiver T Transmitter UART for data communication • Serial data transmission means sending data bits one by one using one wire. • Asynchronous transmission means a data (including one start bit , 8- bit data, and stop bits) can be sent at any time. 5 4
- 6. www.techvilla.org.in Universal asynchronous receivertransmitter : UART • RS232 is a serial communication standard • Since it is asynchronous, no external clock is needed, only 3 wires are required for the simplest RS232 connection {GND, tx(transmit), rx(receive)} 6 5 +10V=Logic 0=space -10V= Logic 1=mark Exercise: Sketch Bit Patterns for character A and B Start 0 1 2 3 4 5 6 7 stop Bit 0 to 7 (least sig. bit first ) time
- 7. www.techvilla.org.inCEG2400 Ch6. SerialInterface -- UART V4b ASCII table 7 6
- 8. www.techvilla.org.inCEG2400 Ch6. SerialInterface -- UART V4b EXAMPLES • Sending ASCII • ‘5’=0x35=0011 0101b 8 7 Start bit=0 10101100(stop bit=1) Least Sign. Bit first What is this code ? The whole ASCII serial character has 10 bits (1 start+8 data + 1 stop bit) Stop bit=1 Oscilloscope Probe T=bit period =1/baud rate
- 9. www.techvilla.org.inCEG2400 Ch6. SerialInterface -- UART V4b If the baud rate is 57600 bits per second Define ‘bit period’ :the amount of time to transmit a logic 1 or 0. (bit period= 1/57600 seconds) • Each bit lasts for (1/Baud rate) seconds 9 8 bit period = 1/baud rate =(1 / 57600) seconds=17.4 us Exercise: What is the “bit period” in seconds if baud rate is 2400?
- 10. www.techvilla.org.in Asynchronous Serial Communication •With asynchronous communication, the transmitter and receiver do not share a common clock Transmitter Receiver+ 1 byte-wide Data Data – 1 byte-wide Data The Receiver φ Extracts the data using its own clock φ Converts the serial data back to the parallel form after stripping off the start, stop and parity bits The Transmitter φ Shifts the parallel data onto the serial line using its own clock φ Also adds the start, stop and parity check bits Add: Start, Stop, Parity Bits Remove: Start, Stop, Parity Bits
- 11. www.techvilla.org.in Asynchronous Serial Communication •Start bit—indicates the beginning of the data word • Stop bit—indicates the end of the data word • Parity bit—added for error detection (optional) • Data bits—the actual data to be transmitted • Baud rate—the bit rate of the serial port • Throughput—actual data transmitted per sec (total bits transmitted—overhead) • Example: 115200 baud = 115200 bits/sec • If using 8-bit data, 1 start, 1 stop, and no parity bits, the effective throughput is: 115200 * 8 / 10 = 92160 bits/sec
- 12. www.techvilla.org.in Asynchronous Serial Communication •Asynchronous transmission is easy to implement but less efficient as it requires an extra 2-3 control bits for every 8 data bits • This method is usually used for low volume transmission
- 13. www.techvilla.org.in Synchronous Serial Communication •In the synchronous mode, the transmitter and receiver share a common clock • The transmitter typically provides the clock as a separate signal in addition to the serial data Transmitter Receiver Data Clock The Receiver φ Extracts the data using the clock provided by the transmitter φ Converts the serial data back to the parallel form The Transmitter φ Shifts the data onto the serial line using its own clock φ Provides the clock as a separate signal φ No start, stop, or parity bits added to data 1 byte-wide Data 1 byte-wide Data
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- 15. www.techvilla.org.in Serial connection usingrs232 protocol
- 16. www.techvilla.org.in RS232 • For asynchronouscommunication. • between two data serial links on a network Between a data─ communication equipment and data terminal equipment. • RS232C a standard protocol used in IBM PC COM ports, keyboard,─ computer-mice and • For the data serial link network in UART bit format
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- 20. www.techvilla.org.in How to set-upavr UART • The first step is to set the baud rate in both, the master and the slave. The baud rate has to be the same for both – master and slave. • Set the number of data bits, which needs to be sent. • Get the buffer ready! In case of transmission (from AVR to some other device), load it up with the data to be sent, whereas in case of reception, save the previous data so that the new received data can be overwritten onto it. • Then enable the transmitter/receiver according to the desired usage.
- 21. www.techvilla.org.in • in UART,there is no master or slave since master is defined by the MicroController, which is responsible for clock pulse generation. • Master and Slave terms occur only in the case of USART. • Master µC is the one which is responsible for Clock pulse generation on the Bus.
- 22. www.techvilla.org.in Baud rate generation •The baud rate of UART/USART is set using the 16-bit wide UBRR register.
- 23. www.techvilla.org.in UBRR register • he16-bit UBRR register is comprised of two 8-bit registers – UBRRH (high) and UBRRL (low). • The USART Baud Rate Register (UBRR) and the down-counter connected to it functions as a programmable prescaler or baud rate generator. • The down-counter, running at system clock (FOSC), is loaded with the UBRR value each time the counter has counted down to zero or when the UBRRL Register is written. • A clock is generated each time the counter reaches zero.
- 24. www.techvilla.org.in Calculating baud rateand UBRR value
- 25. www.techvilla.org.in •BAUD = BaudRate in Bits/Second (bps) •Bps = Bytes/Second, whereas bps = Bits/Second) •FOSC = System Clock Frequency (1MHz) (or as per use in case of external oscillator) •UBRR = Contents of UBRRL and UBRRH registers
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- 27. www.techvilla.org.in FRAME STRUCTURE • USARTcommunication uses special protocol to transmit data reliable. It consists of several parts: • 1 start bit; • 5,6,7,8 or 9 data bits; • no, even, or odd parity bit; • 1 or 2 stop bits.