Measurement Computing Personal488 rev.3.0 For DOS & Windows 3.Xi - Manual (Page 221)

10D. Getting Started II. SOFTWARE GUIDES - 10. Driver488/W31
II-206 Personal488 User’s Manual, Rev. 3.0
Duplicate Device Names
Duplicate device names are most often used in systems that consist of several identical sets of
equipment. For example, a test set might consist of a signal generator and an oscilloscope. If three test
sets were controlled by a single computer using three separate IEEE 488 interfaces, then each signal
generator and each oscilloscope might be given the same name and the program would specify which
test set to use by opening the correct interface (
OpenName(“IEEE”) for one, OpenName(“IEEE2”)
for the other), or by using the interface names when opening the devices
(
OpenName(“IEEE:GENERATOR”) for one and OpenName(“IEEE2:GENERATOR”) for the other).
Unique names are appropriate when the devices work together, even if more than one interface is used.
If two different oscilloscopes, on two different interfaces are used as part of the same system, then they
would each be given a name appropriate to its function. This avoids confusion and eliminates the need
to specify the interface when opening the devices.
Access of Multiple Interfaces
If the computer only has one IEEE 488 interface, then there is no confusion; for every external device
is known to be on that interface. As noted above, duplicate device names on one interface are not
recommended; if they exist, the most recently defined device with the requested name will be used.
When more than one interface is available and duplicate names appear on different interfaces, the
following rules apply.
1. If the external device name is specified without its interface name, then any external device with
that name may be used. If more than one external device has that name, then the choice of which
particular external device is not defined.
2. If the external device name is specified with its interface name prefixed, then that external device
on that hardware interface is used. If that external device is not attached to the specified hardware
interface, then an error occurs.
Example
Assume there are three IEEE 488 interfaces: IEEE , IEEE2 , and IEEE3 controlling multiple devices:
SCOPE (on IEEE ), DA (on IEEE2 ) and DA (on IEEE3 ). Since there are two external devices, both
named DA , their full name must be used to specify them.
We can communicate with the external devices, according to the two rules above.
scope = OpenName (“SCOPE”) ; // SCOPE on IEEE (Rule 1)
da = OpenName (“DA”) // DA on IEEE2 or IEEE3 (not specified)
da = OpenName (“IEEE2:DA”) ; // DA on IEEE2 (Rule 2)
scope = OpenName (“IEEE2:SCOPE”); // Error (not IEEE:SCOPE) (Rule 2)
10D. Getting Started
Topics
•
Introduction................................................................................... II-206
C Languages................................................................................................. II-206
Visual Basic ................................................................................................. II-206
•
C Languages................................................................................... II-206
Required Headers ........................................................................................ II-206
Required Libraries ...................................................................................... II-207
•
Visual Basic.................................................................................... II-207
Required Files .............................................................................................. II-207