[time-nuts] General Purpose Instrument Troubles

Brooke Clarke brooke at pacific.net
Fri Nov 26 14:50:49 EST 2004

Hi Bill:

488.2 is backward compatible with 488.

But instruments differ in a couple of respects:

(1) older instruments were driven by computers of equal vintage and 
sometimes when using a more modern computer there is not enough time for 
the instrument to respond.  You can allow for this by adding a wait in 
your software after you send any command or before you ask for a response.

(2) there are different ways that the instrument recognizes the end of a 
command string.  Some older instruments may want to see <carriage 
return> and <line feed> at the end of each command.  In addition they 
may or may not need the <End Or Identify> hardware tag on the last byte.

I don't understand you comment about the "ID string that the NI 
controller is using".
Early instruments used what's called "R2D2" commands and the newest 
instruments use what's called SCPI commands that are generic.  The R2D2 
commands were instrument model number specific.  For example an 
instrument may respond to ID or ID? with whatever the manufacturer 
wanted it to say.  As part of 488.2 there are a number of generic 
commands, like *IDN? to get ID information from an instrument which 
responds with the same information in the same order for each instrument.

For some more on this see:

Have Fun,

Brooke Clarke

w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml

Bill Hawkins wrote:

>Have a Racal-Dana 1992 counter with a GPIB interface.
>Also have a National Instruments 488.2 ISA bus card with
>software dated July 2000, with PDF manuals. Found a PDF
>manual for the 1992 on the net and focused on the GPIB
>Hooked them up with an IBM 365 PC running Win98. NI 488.2
>controller sees the 1992. 1992 reacts when NI sends ID
>string, but nothing else works - all result in timeout.
>1992 manual says it is using 1978 vintage GPIB, and I cannot
>find the ID string that the NI controller is using.
>I suspect that my problem is compounded incompatibilities.
>Is 488.2 compatible with the earlier 488?
>Any insight appreciated.
>Bill Hawkins
>time-nuts mailing list
>time-nuts at febo.com

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