The old saying is
"The clothes makes the man." In the same way, we can also say
"The driver makes the instrument." By changing the driver, the
instrument may take on a new, improved personality.
Overview: What is a driver?
Just what is a "driver" for an instrument? We
see the term "driver" being used to describe many pieces of software
DSCPI Downloadable SCPI drivers for the Command Module, CSCPI drivers, VXIplug&play
drivers. And the list goes on. They are all drivers, because they all help to
control the instrument. Many VXI instruments are "Register based".
That is, the manufacturer provides a list of registers, or addresses, and tells
what happens when certain values are written to those addresses, or tells what
to expect when you read the values at those addresses. If it is a switch card,
for instance, writing a "1" to bit 5 of address 32 may close switch
number 5. (But you better remember what the other bits need to be too.) If it is
a voltmeter, sending a "2048" to address 32 may tell it to use the 8
volt range. There is no way to tell without the register map. Now, such detail
gives the programmer fine detailed control over the instrument, but it also
makes programming the instrument difficult. It is like getting into a taxi and
instructing the driver how to step on the gas and turn the steering wheel to get
to your destination. It is much easier to just say "1020 Main Street"
and let the driver do the rest. It is the same for instruments to tell the
driver what switch to close or what voltage measurement to make, and let the
driver do the rest.
A new road to follow
But just as the taxi driver can make decisions over what
route to take, so too instrument drivers can decide how to control the
instrument. The taxi driver that knows the good roads will get you there faster
than the one who does not. When a new road is built, the taxi driver must learn
about it and know when to use it. So too, when new interfaces are developed, the
drivers must be changed in order to use it better. Techniques that were the
right way to go before may no longer be good. Such is the case with FireWire.
When the first instrument drivers were developed for
Hewlett-Packard VXI instruments, the only interface available was the Command
Module. It was limited in memory, but had fast access to the VXI backplane. The
drivers were written to use memory sparingly, and to read the instrument
registers often. New computers, embedded controllers and FireWire have changed
all that. Memory has become cheap and plentiful. And in the case of FireWire,
with its 150 m Sec latency, access to the VXI backplane needs to be limited. In
reviewing some of the older instrument drivers, the following areas for
improvement in the drivers were found.
Using these improvements, the E1458A driver's performance
with the FireWire interface can increase as much as a factor of 10. (Revision
G.05.05 hpdig_i32v.dll) It is well worth the try. For simple measurements, the
speed of the E1411 can be almost doubled. (Revision G.08.00 hpe132632v.dll)
A New Driver for a New Personality
Improving the driver speed for a new interface is one
thing that can be done by changing a driver. Another thing that can be done is
to change the feature set of the instrument, thus giving the instrument a whole
new personality. Such is the case with the E8460A 256-channel switch card.
Originally this switch card was designed to be "stand-alone". That is,
it was to be an instrument by itself. This simplified the driver development for
the switch card. Unfortunately, it also made it difficult to form a scanning
voltmeter with the E1411B/E8460A combination. The voltmeter and the switch card
needed to be addressed as two separate instruments by adding complexity and
overhead to the customer software. A decision was made to add the E8460 to
"switchbox", or SWITCH. This gives the E1411B voltmeter the ability to
use this switch automatically in a Scanning Voltmeter. By adding the E8460A to
the SWITCH and VOLTMTR drivers, a "new set of clothes" is provided for
the E8460A. The same hardware can now be used in a different way, just by using
it with new software. This greatly simplifies programming and speeds up
instrument operation. The driver indeed makes the instrument.
What Revision Number is that?
Where Can I Get a Copy?
The latest copies of these drivers are available at the
Agilent Technologies customer WWW site:
http://ftp.agilent.com/pub/mpusup/drivers.html
If you do not have Internet access, the drivers can be obtained by contacting
your country support organization. Ask for the Agilent "Universal
Instrument Drivers" CD Revision A.08.00 or later.