1. The Principle of Electronic Data Serial and Parallel Data Communication Transmission Rate Bandwidth Bit Rate Parity bits

2. The Principle of Electronic Data Involves sending and receiving information data from one computer or data processing device to another. Involves sending and receiving information data from one computer or data processing device to another. Examples E-mail, Supermarket EPOS (Electronic Point of Sale) Terminals, Cash Dispensers, Facsimile Video Conferencing.

3. Serial Data Communication. Serial Data Transmission: bits are sent via an interface one bit at a time over a single wire, from the source to the destination. Serial Data Transmission: bits are sent via an interface one bit at a time over a single wire, from the source to the destination. 0 1 0 1 1 0

4. Serial Data Communication. (An example of a very high data transfer rate is through the use of fibre-optic cable, which has a data transfer rate of 1000Mbs per second.) (An example of a very high data transfer rate is through the use of fibre-optic cable, which has a data transfer rate of 1000Mbs per second.)

5. Parallel Data Communication. Parallel Data transmission is used inside the computer (using various computer buses) and for short distances (a few metres), so to prevent data being misread. Parallel Data transmission is used inside the computer (using various computer buses) and for short distances (a few metres), so to prevent data being misread. 010110010110

6. Parallel Data Communication. A parallel port can send 8, 16, or 32 bits simultaneously down separate lines. A parallel port can send 8, 16, or 32 bits simultaneously down separate lines. A printer uses the parallel port. A printer uses the parallel port.

7. Parallel Data Communication. Limited to short distances of a few metres, e.g. between a computer and printer. Limited to short distances of a few metres, e.g. between a computer and printer. Limitation because it is very difficult to produce copper wire with the exact same resistance. Limitation because it is very difficult to produce copper wire with the exact same resistance. Simultaneous transmission of data over distances can result in skewing of data (bits not arriving in parallel) due to varying resistance of wires. Simultaneous transmission of data over distances can result in skewing of data (bits not arriving in parallel) due to varying resistance of wires.

8. Transmission Rate The Baud Rate is named after Baudot who did a lot of work with electronic signals. The Baud Rate is named after Baudot who did a lot of work with electronic signals. The Baud Rate is the rate that the voltage changes and the speed at which the data is transmitted serially. The Baud Rate is the rate that the voltage changes and the speed at which the data is transmitted serially. 0 1 0 1 1 0

9. Transmission Rate The sender will generate one voltage to represent 1 and a different voltage to represent 0. The sender will generate one voltage to represent 1 and a different voltage to represent 0. The sender has a clock which transmits bits at regular intervals. The sender has a clock which transmits bits at regular intervals. At any point in time there will be a number of bits being carried along the wire. At any point in time there will be a number of bits being carried along the wire. Generally one baud is one bit per second. Generally one baud is one bit per second.

10. Baud Rate Framing bits have to be transmitted with each character to provide Framing bits have to be transmitted with each character to provide –start and stop bits, –error detection –and communication controls. A baud rate 56K does not mean that 7000 characters per second will be transmitted: the figure will be lower. Why?

11. Bandwidth Bandwidth measures signal changes per second, and is measured in Baud. Bandwidth measures signal changes per second, and is measured in Baud. When a signal is transmitted along a wire (or any other medium) it is reluctant to travel as a square since waves are naturally in the form of sine waves (analogue signals).

12. Bandwidth High Frequency Low Frequency All media are capable of transmitting a set of waves that have a range of frequencies.All media are capable of transmitting a set of waves that have a range of frequencies. The frequency of the wave is the rate at which the wave repeats itself.The frequency of the wave is the rate at which the wave repeats itself. The higher the bandwidth the greater the amount of data that can be transmitted.

13. Bandwidth The range of the frequencies that a medium can transmit is the bandwidth. The range of the frequencies that a medium can transmit is the bandwidth. If the bandwidth is wide then more data can be transmitted. If the bandwidth is wide then more data can be transmitted. –A normal telephone wire has low bandwidth so it is not possible to transmit large amounts of data. –An optical fibre has a high bandwidth and is able to transmit large amounts of data.

14. Bit Rate Is the term given to the rate that the bits are transmitted. Is the term given to the rate that the bits are transmitted.  Remember the baud is the rate the voltage changes. If the voltage changes 10 times every second the baud is said to be ten. If the voltage changes 10 times every second the baud is said to be ten.

15. Bit Rate If four voltages were generated instead of two, each change in signal could be used to represent two bits. If four voltages were generated instead of two, each change in signal could be used to represent two bits. Therefore, if the signals are transmitted 10 times a second, the baud rate is still 10 but 20 bits per second are being transmitted. Therefore, if the signals are transmitted 10 times a second, the baud rate is still 10 but 20 bits per second are being transmitted.

16. Remember Baud Rate refers to the rate that the signals are transmitted along a wire. Baud Rate refers to the rate that the signals are transmitted along a wire. Bit Rate refers to the rate that bits are transmitted. Bit Rate refers to the rate that bits are transmitted.

17. Parity bits A parity bit is an extra bit added to the character code A parity bit is an extra bit added to the character code Set to 0 or 1 Set to 0 or 1 so that total number of 1’s in code is even, for even parity so that total number of 1’s in code is even, for even parity or total number of 1’s in code is odd, for odd parity. or total number of 1’s in code is odd, for odd parity.

18. Parity bits Parity checks are used to determine whether the parity of a data item is correct when it is being sent to or from an input, output or storage device, or being sent over a communications line. Parity checks are used to determine whether the parity of a data item is correct when it is being sent to or from an input, output or storage device, or being sent over a communications line. Odd parity will detect the failure of a transmission line, because all the bits will then be set to zero. Odd parity will detect the failure of a transmission line, because all the bits will then be set to zero. Note that the character code, including the parity bit, is an example of a self checking code. Note that the character code, including the parity bit, is an example of a self checking code.

19. Parity bits Add a parity bit to the end (LHS) of each of the following codes to maintain odd parity: 110101 001101 Add a parity bit to the end (LHS) of each of the following codes to maintain odd parity: 110101 001101 Remember: Remember: –Set to 0 or 1 –so that total number of 1’s in code is even, for even parity –or total number of 1’s in code is odd, for odd parity.

20. Parity bits The ASCII codes for The ASCII codes for P is 1010000 P is 1010000 Q is 1010001 Q is 1010001 In an even parity transmission system what will be the value and parity bit for P and Q? In an even parity transmission system what will be the value and parity bit for P and Q?

21. Synchronous and Asynchronous transmission Two types of serial mode for sending data Asynchronous transmission one character at a time, with a start and stop bit and parity bit sent with each character. one character at a time, with a start and stop bit and parity bit sent with each character. For each character sent, 10 bits are transmitted For each character sent, 10 bits are transmitted Start bit alerts the receiving device and synchronises the clock inside the receiver ready to receive the character. Start bit alerts the receiving device and synchronises the clock inside the receiver ready to receive the character. Baud rate at receiving end has to be set up be same as senders. Baud rate at receiving end has to be set up be same as senders. Usually used by PC’s, fast and economical for relatively small amounts of data. Usually used by PC’s, fast and economical for relatively small amounts of data.

22. Synchronous transmission Enables whole blocks of data to be sent in timed sequences Enables whole blocks of data to be sent in timed sequences Timing signals (usually computer’s internal clock) control rate of transmission Timing signals (usually computer’s internal clock) control rate of transmission There is no need for start and stop bits to accompany each character. There is no need for start and stop bits to accompany each character. System is less error prone than asynchronous System is less error prone than asynchronous Much faster – usually used on mainframe computers Much faster – usually used on mainframe computers

23. Handshaking The exchange of signals between devices to establish their readiness to send or receive data. The exchange of signals between devices to establish their readiness to send or receive data. –E.g. between a computer and printer One method of ensuring both sender and receiver are ready before transmission begins One method of ensuring both sender and receiver are ready before transmission begins The conversation between two devices along lines of:- The conversation between two devices along lines of:- –Device 1: “Are you ready to receive some data?” –Device 2: “Yes, go ahead.” –Device 1: (sends data) –Device 2: “Message received, thanks!”