7. Peripherals

7.3 Data transmission

Computer Studies (AL)

Content Concepts of protocol Serial and parallel transmission Synchronous and asynchronous

transmission Simplex and duplex modes Multiplexing Transmission errors and parity checking

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 5th edition (2002)”, McGraw Hill

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.

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.

Asynchronous transmission The simplest scheme for serial

communications is asynchronous transmission using a technique called start-stop.

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.

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.

Serial transmission Serial data transmission is the transmission

of one bit at the time through a single wire. Common use: Modem

Modem – Modulator-Demodulator It is a device used to modulate digital

signals to analog signals and demodulate analog signals to digital signals.

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.