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Embedded Systems: Explanation
General non-technical explanation
What is an embedded system?
Embedded systems compared with commercial systesm
Categories of Embedded system and Year2000 Risks
Applications of embedded systems
Categorisation in relation to checking
Notes
Personal Computers
High Intengrity Systems
What is an embedded system?
A general purpose definition of embedded systems is that they are devices
used to control, monitor or assist the operation of equipment, machinery or
plant. "Embedded" reflects the fact that they are an integral part of the
system. In many cases their embeddedness may be such that their presence is
far from obvious to the casual observer and even the more technically
skilled might need to examine the operation of a piece of equipment for some
time before being able to conclude that an embedded control device was
involved in its functioning. At the other extreme a general purpose computer
may be used to control the operation of a large complex processing plant,
and its presence will be obvious.
All embedded systems are computers. Some of them are however very simple
devices as compared with a PC. The simplest devices consist of a single
microprocessor (often called a "chip" ) which may itself be packaged with
other chips in a hybrid or Application Specific Integrated Circuit (ASIC).
Its input comes from a detector or sensor and its output goes to a switch or
activator which (for example) may start or stop the operation of a machine
or, by operating a valve, may control the flow of fuel to an engine.
The very simplest embedded systems are capable of performing only a single
function or set of functions to meet a single predetermined purpose. In the
more complex systems the functioning of the embedded system is determined by
an application program which enables the embedded system to do things for a
specific application. The ability to have programs means that the same
system can be used for a variety of different purposes. In some cases a
microprocessor may be designed in such a way that application software for a
particular purpose can be added to the basic software in a second process,
after which it is not possible to make further changes: this is sometimes
referred to as firmware.
Embedded systems compared with commercial systems
The Year2000 problem in embedded systems differs from the problem in
commercial / database / transaction processing systems (often referred to as
IT systems) in a number of ways. Firstly the user's problem may much lie
much deeper than packages or applications software. it may lie in and be
inseparable from systems and operating software and from hardware, i.e. in
the platform on which the application software is based. When users of IT
systems have hardware or operating software problems they can and should be
made the concern of the computer supplier: typically, this is not the case
with microprocessors and devices based on them.
Secondly in embedded systems the concern is often with intervals rather than
with specific dates: the need may be for an event to occur at 100-day
intervals rather than on the 5th day of each month. This has the implication
that Year2000 problems may reveal themselves both before and for some time
after 1 January 2000 and not at all on the date itself. On the other hand
there is a possibility that devices with cycles which are measured in hours,
and minutes (or even seconds) may be affected by the problem because year
numbers are the basis of time calculations. In such systems the effect may
not be evident on (as it were) the stroke of midnight but will arise
sometime during the following twenty-four hours.
Categories of Embedded system and Year2000 Risks
All of these may be in your plant and equipment and in your products.
Individual microprocessors
Small assemblies of microprocessors with no timing function
Subassemblies with a timing function
Computer systems used in manufacturing or process control
Individual microprocessors
These may be found in small devices such as temperature sensors, smoke and
gas detectors, circuit breakers, etc. It is highly unlikely but nevertheless
possible that these will be affected. If they are (1) it will not be evident
after the date and (2) the only possible action is to replace the
microprocessor. If in doubt you should consult the supplier.
Small assemblies of microprocessors with no timing function
These may be found in flow controllers, signal amplifiers, position sensors
and valve actuators. It is unlikely that these will be affected. However
they may depend on a clock for their internal operation which might be
affected by the Year2000 problem. This is unlikely to reveal itself before
the date. If you suspect there may be a problem (there are a number of
things you may wish to think about , you should consult the supplier
[Further information will become available].
Subassemblies with a timing function
Special devices such as switchgear, controllers (e.g. for traffic),
telephone exchanges, lifts, data acquisition and monitoring systems,
diagnostic and real time control systems may fall into this category. These
systems may be local elements in a larger system to which they pass data
from collected from their sensors. They may incorporate a PC, and may
involve some kind of database (e.g. of events). In these the Year2000
problem may affect their systems or application software; the database; and
the networks and data transmission systems they use to communicate with the
larger system. The error may become apparent before the year 2000 (because
the system may attempt to make a record of when next a particular action
should take place), on the date 01/01/2000 and for some time after that. You
need to consult the supplier of the particular system and those responsible
for the integration of the larger system. They in turn may need to consult
their suppliers. Note that in these cases attention needs to be paid (1) to
the components of the particular system, (2) to the system as a unit and (3)
to the larger system of which it is a part. This is because although each
part may function correctly when examined separately this is not a guarantee
that the whole will work properly when the parts are assembled into a device
or system.
Computer systems used in manufacturing or process control
This relates to cases where the computer is connected to plant, machinery or
equipment in order to control it. It includes automated logistics/storage
and delivery systems. These systems are liable to be affected in exactly the
same way as commercial data processing systems, because of course the
hardware and the systems software are the same, and because the applications
software may have been developed along similar lines. Note also that there
is a developing trend to link process control with business systems (for
example to enable sales figures and stock levels to determine automatically
which quantities of which products should be produced). This means that
there is the possibility of knock-on effects from one to the other. In these
instances it is probable that enquiries need to begin in-house with the
engineers and the IT departments, or if appropriate, the facilities manager.
There are also off-the-shelf hardware/software packages which fall into this
category; in their case the supplier needs to be consulted. See Checking
Software.
Applications of embedded systems
Embedded controllers may be found in the following kinds of system. The list
does not claim to be exhaustive. Information about other examples would be
welcomed. Please send these to: 2000risk@iee.org.uk
Office systems and mobile equipment :
* Telephone systems
* Faxes
* Copier
* Time recording systems
* Mobile Telephones
* Still and video cameras
Building systems:
* Backup lighting and generators
* Fire control systems
* Heating and ventilating systems
* Lifts, elevators, escalators
* Security systems
* Security cameras
* Safes and vaults
* Door locks
Manufacturing and Process Control
* Manufacturing plants
* Water and sewage systems
* Power stations
* Power grid systems
* Oil refineries and related storage facilities
* Bottling plants
* Automated factories
* Simulators
* Test equipment used to program, maintain and test control systems
Medical diagnostics, monitoring and life support
* Heart defibrillators
* Pacemaker monitors
* Patient information systems
* Patient monitoring systesm
* Pharmaceutical control and dispensing systems, e.g. infustion pumps
* X-ray equipment
Transport:
* Aeroplanes
* Trains
* Buses
* Marine craft
* Automobiles
* Air Traffic Control Systems
* Signalling Systems
* Radar Systems
* Traffic Lights
* Ticketing systems/machines
* Car parking and other meters
Communications:
* Telephone exchange
* Cable systems
* Telephone switches
* Satellites see also Global Positioning System (GPS) problem
* Data Switching Equipment (X.25, SMDS, Frame Relay, etc.)
Banking, finance and commercial
* Automated teller systems
* Credit card systems
* Point of sale systems including scanner/cash systems
Testing and Diagnostic Systems
Others
* Energy Metering
* Environmental Monitoring Equipment
This is a dynamic and comments and additions are welcome.
Categorisation in relation to checking
In relation to possible actions there are two distinct categories of
embedded system:
those based on a "normal" computer where the software can be examined or
modified. In some cases only the supplier of the hardware or system and not
the user company may be able to make modifications. Checking of systems
where the hardware is accessible and modifiable is dealt with under the
heading Checking software
those whose software is inaccessible and / or cannot be modified: this
includes (a) items where the software is embedded as firmware and (b) items
where it may be physically possible to access the software but impractical
to modify it because of the form in which it is written. In either case
there are almost certainly instances where the hardware used is not the
hardware specified or where the embedded software is different from the
software as originally specified. Checking systems for the presence of these
items is discussed in the section Systems/hardware checking .
Software may need to be considered in three categories with regard to
modification:
(a) Sytems software suppied by the computer manufactorer ,whose modification
by you, may invalidate the terms of your contract with the supplier.
(b) Software supplied by a third party. Modification of code in a shrink
wrapped package may invalidate the terms and conditions of the sale.
Conversely if you have accepted bespoke software from a supplier who no
longer has any maintenance obligations, you are likely to be able to modify
it. However if extensive modifications have been made, it may be more
difficult to persuade the supplier to accept a new contract for further
modifications.
(c) Software developed in-house for which you have responsibility
Embedded Systems: application categories
Multi-loop control and monitoring - DCS, SCADA, telemetry
Panel mounted devices - Control, display, recording and operations
Safety and security - Alarm and trip systems, fire and gas systems,
buildings and facilities security
Field devices - measurement, actuation
Analytical systems - Laboratory systems; online/ plant systems
Electrical supply - supply, measurement, control, protection
Tools - for design, documentation, testing, maintenance
list of microprocessors
Notes
Software is the name for the instructions used to control the operation of a
computer. A set of instructions for a particular purpose is called a
program. If you have written a macro for a word processor or a spreadsheet
you have in fact written a program. Programs which make it perform functions
for a particular purpose, like your macro, or the word processor itself, are
called applications programs or applications software. Software is also used
to make the computer itself work, i.e. to control the interoperation of its
various parts. This is system software.
A computer in principle consists of at least an input device, a device for
processing the data which is input and another device for the output, i.e.
for the results. In the standard personal computer, the keyboard is the
device for entering data and the screen is the means for the display (or
output) of the results of processing that data. The computer processor
itself is contained in the box on which the screen usually sits.
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Document last checked: 6th August 1997
klewis@iee.org.uk
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c Institution of Electrical Engineers
From: iee.org.uk |
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