Transcript Digital to Analogue Conversion

Computer Systems and
Networks
Chapter 6: Interfacing to the physical
world
Use with Computer Systems and Networks
by Blundell, Khan, Lasebae and Jabbar ISBN 978-184480-639-3
© 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 978-184480-639-3
© 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 978-184480-639-3
© 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 978-184480-639-3
© 2007 Middlesex University Press
A two-bit DAC with an output in the range 03 volts.
Use with Computer Systems and Networks
by Blundell, Khan, Lasebae and Jabbar ISBN 978-184480-639-3
© 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 978-184480-639-3
© 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 978-184480-639-3
© 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.
Use with Computer Systems and Networks
by Blundell, Khan, Lasebae and Jabbar ISBN 978-184480-639-3
© 2007 Middlesex University Press