Use with Computer Systems and Networks by Blundell, Khan, Lasebae and Jabbar ISBN © 2007 Middlesex University Press Computer Systems and Networks Chapter 6: Interfacing to the physical world

Use with Computer Systems and Networks by Blundell, Khan, Lasebae and Jabbar ISBN © 2007 Middlesex University Press Learning Objectives: Discuss the need for both input and output devices; Describe the operation of analogue-to-digital and digital-to-analogue converters; Distinguish between various forms of interaction device; Discuss the operation of the ‘pixmapped’ graphics display and Cathode Ray Tube; Discuss the use of several display metrics.

Use with Computer Systems and Networks by Blundell, Khan, Lasebae and Jabbar ISBN © 2007 Middlesex University Press Representation of an 8-bit digital-to-analogue converter.

Use with Computer Systems and Networks by Blundell, Khan, Lasebae and Jabbar ISBN © 2007 Middlesex University Press A DAC is used to generate an analogue signal. This is amplified and applied to a loudspeaker. In this way digital signals may be used to generate simple sounds.

Use with Computer Systems and Networks by Blundell, Khan, Lasebae and Jabbar ISBN © 2007 Middlesex University Press A two-bit DAC with an output in the range 0- 3 volts.

Use with Computer Systems and Networks by Blundell, Khan, Lasebae and Jabbar ISBN © 2007 Middlesex University Press A digital-to-analogue convertor can be used to implement an analogue-to-digital convertor. Additional hardware is, however, required in the form of a comparator. This device compares the analogue input voltage with the output from the digital-to-analogue convertor, see text for details.

Use with Computer Systems and Networks by Blundell, Khan, Lasebae and Jabbar ISBN © 2007 Middlesex University Press Repeatedly incrementing the binary value applied to a DAC produces a ramp (‘staircase’) output signal.

Use with Computer Systems and Networks by Blundell, Khan, Lasebae and Jabbar ISBN © 2007 Middlesex University Press Typically a keyboard contains ~100 keys. Rather than connecting each key individually to the keyboard scanner, a coding technique is commonly used. The connections (wires) illustrated in the diagram permit the 100 keys to be connected to the keyboard encoder by means of 10 output wires and 10 input wires. The horizontal and vertical wires drawn in the diagram are not physically in contact, but are connected together by the keyboard keys that are electrically located at the points where the vertical and horizontal wires cross over one another.