1. 7. Peripherals 7.3 Data transmission Computer Studies (AL)

2. Content Concepts of protocol Serial and parallel transmission Synchronous and asynchronous transmission Simplex and duplex modes Multiplexing Transmission errors and parity checking

3. Reference Leung Man Kit, “Pui Ching Middle School AL Computer Studies Notes. (2002)” Douglas A. Downing PhD, “Dictionary of Computer And Internet Terms (2000)”, Barron’s. Carl Hamacher, “Computer Organization 5 th edition (2002)”, McGraw Hill

4. Protocol A protocol is a set of formal rules describing hoe to transmit data. Low level protocols define the electrical and physical standards to be observed bit-and-byte-ordering the transmission and error detection correction of the bit stream. High level protocols deal with the data formatting, including the syntax of messages, the terminal to computer dialogue, character sets, sequencing of messages, etc.

5. Asynchronous transmission Most computer use this method The terminal or the computer is free to transmit any number of characters at any time. The bit constituting each character are transmitted at a fixed rate, but the pauses between characters can e of any duration.

6. Asynchronous transmission The simplest scheme for serial communications is asynchronous transmission using a technique called start- stop.

7. Synchronous transmission Synchronous transmit data in packets of more than one character. This is faster than asynchronous communication because there is no need for a start bit or stop bit on each individual character.

8. Parallel transmission Parallel data transmission is the transmission of several bits at the same time over separate wires. It is common for a microcomputer to have a parallel port that is connected to a printer.

9. Serial transmission Serial data transmission is the transmission of one bit at the time through a single wire. Common use: Modem

10. Modem – Modulator-Demodulator It is a device used to modulate digital signals to analog signals and demodulate analog signals to digital signals.

11. Simplex, half duplex and full duplex Simplex allows transmission in one direction only. Half duplex (HDX) allows transmission in either direction, but not at the same time. Full duplex (FDX) allows simultaneous transmission in both directions.