Hardware Reference
In-Depth Information
Specifying hardware
and software
When specifying hardware and software to be used in a given PC bus applica-
tion, it is essential to adopt a 'top-down' approach. An important first stage in
this process is that of defining the overall aims of the system before attempt-
ing to formalize a detailed specification. The aims should be agreed with the
end-user and should be reviewed within the constraints of available budget
and time. Specifications should then be formalized in sufficient detail for the
performance of the system to be measured against them and should include
such items as input and output parameters,
response time,
accuracy,
and
resolution.
Having set out a detailed specification, it will be possible to identify the
main hardware elements of the system as well as the types of sensor and output
device required (see Chapter 9). The following checklist, arranged under six
major headings, should assist in this process:
1
Performance specification
•
What are the parameters of the system?
•
What accuracy and resolution are required?
•
What aspects of the process are time critical?
•
What environment will the equipment be used in?
•
What special contingencies should be planned for?
•
What degree of fault tolerance is required?
2
I/O devices
•
What sensors will be required?
•
What output devices will be required?
•
What I/O and signal conditioning boards will be required?
•
Will it be necessary to provide high-current or high-voltage drivers?
•
Should any of the inputs or outputs be optically isolated?
3
Displays and operator inputs
•
What expertise can be assumed on the part of the operator?
•
What alarms and status displays should be provided?
•
What inputs are required from the operator?
•
What provision for resetting the system should be incorporated?
4
Program/data storage
•
What storage medium and format are to be employed?
•
How much storage space will be required for the operating system and/or
control program?
•
How much storage space will be required for data?
•
How often will the control program need updating?
•
Will stored data be regularly updated during program execution?
•
What degree of data security and integrity must be achieved?
5
Communications
•
What existing communications standards are employed by the end-user?
•
Will
a
standard
serial
data
link
based
on
RS-232
be
sufficient
or
will a faster,
low-impedance serial data communications standard be
needed?
•
What data rates will be required?
•
What distances are involved?
•
Will it be necessary to interface with automatic test equipment?
•
Will a networking capability be required?
