Re: HPIB bus commands

From: Larry Mollica (
Date: 2004-04-19 09:45:47

>From: Larry Mollica; on Date: Monday, April 12, 2004, at 03:57 PM
>I think that you might be confusing "bus commands" with "device commands."

I confuse lots of stuff! :)

>TALK/UNTALK and LISTEN/UNLISTEN are bus-commands.  But, an instruction to
>unlock an instrument's front-panel would be a device-command (or an

THAT would have made sense, but...

>So now, the question is:
>1) are device-commands sent as "normal data,"
>2) or are they, too, sent with ATN set to "active."

The answer is; both. A few examples;

Most of the functions, like say, entering a frequency value, are 
normal data, as in a PRINT# command. We have been able to get this 
kind of stuff (mostly) working.

  PRINT#1, "A1";
will for example select a specific relay in an HP switch box.

But others are listed as "bus commands" to be sent with ATN low (as I 
recall). Again, right now I don't have the manuals handy.

For some reason these functions include doing things like unlocking 
the panel controls (which are locked upon sending any of the data 
commands), or lock/unlock the instrument the reset button. Those are 
a few things I can recall off hand, don't remember the commands. If 
the characters HP lists as "bus commands" are sent in a PRINT#, they 
do nothing.

I don't know why HP thought that certain things deserved to be bus 
commands, while most of the instrument control is done with regular 
data. Maybe they had a reason, but for us it's just a big pain.

>If the answer is (1), then PRINT# probably should work.  But, if the answer
>is (2), then you might be able to use BASIC's OPEN statement.
>I vaguely remember that OPEN keeps ATN set to "active" while it sends the
>file-name string.  If I'm correct, then you could pretend to open (and
>close) a file.  You would use the device-command that you want to send as
>the name of that phony file.

That should be easy to try. I will give it a shot next weekend maybe, thanks.

One potential problem is some of the HP bus commands were control 
characters, although many were printable. I'll have to get my hands 
on manuals before I can tell if this method would do us any good.

>More questions just occurred to me:  How does Commodore's definition of
>"device number" compare to Hewlett Packard's definition?  Is the CBM even
>able to choose one of your instruments?!

Pretty much the same, although seems like no two HP manuals document 
the remote control subject in the same way. I'm guessing they were 
written by different engineers who were mad at each other.

If you set the HP dip switch to a value of 5, then
OPEN 1,5
will give you control. (The front panel locks upon the first PRINT#, 
and stays that way until you turn off or reset the instrument. Either 
of which destroy any setup the PET may have done.)

One interesting tidbit, the OPEN statement allows 4-31 as IEEE488 
addresses, with 0-3 used for PET internal devices. But we found (ok, 
by accident), that you can address IEEE488 addresses below 4 by using 
values over 31, like
OPEN 1,34
to talk to IEEE488 bus address 3. The extra bit seems to be ignored 
by all parties, and no ill effects observed (so far).

Thanks again for your thoughts.


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