[Linux-gpib-general] Emulating a plotter?

[John A. N. <jr...@fe...>]

I wonder if anyone has done this, or can provide some starting hints to 
point me in the right direction...

I'd like to create a tool that will emulate an HP plotter and create a 
graphics file output.  I have several instruments that have a "plot" 
function that dumps a screen trace to the GPIB port, and I'd like to 
emulate that -- basically, I'd run the capture program on the Linux box, 
push the "PLOT" button on the instrument (or issue a GPIB command), and end 
up with a PNG file of the dump.

I've already written a graphics backend that will handle the image 
rendering, but I'm not sure how to start with the GPIB side of things -- 
how do I make the PC look and respond like a plotter when the instrument 
sends the plot command?

Here's a bit of description from an HP manual when using the "PLOT" key: 
The plotter/printer must be addressed to listen-only and all controllers 
must be removed from the bus... When the PLOT key is pressed, the 
instrument checks to make sure there is at least one listener and no 
controllers on the bus, and if so, begins sending HP-GL commands to the 
device.  Unfortunately, there's no description of what happens when the 
plot is complete.  It appears from some other parts of the documentation 
that the device is supposed to assert SRQ when it's finished with the dump, 
but you need to check the status without doing a serial poll as that would 
abort the plot in process.  Alternatively it may work to snoop on the 
transfer and look for the EOI signal to be true.

Thanks for any pointers you might have... once again, I'm delving in way 
beyond my limited knowledge of GPIB.

John
jr...@fe...

PS --  I've written screen capture programs "the hard way" for the HP 3585B 
and HP 8569B analyzers; these use GPIB commands to get trace data and 
instrument settings and prepare PNG plots.  They work really well, but it's 
a pain to write a separate program for each instrument; a plotter emulator 
seems like a useful way around this problem.

If you're interested in the current programs, they're written in perl and 
are available at ftp://ftp.febo.com/pub/n8ur_programs/ with descriptions 
available at http://www.febo.com/geekworks/data-capture/hp3585b.html and 
http://www.febo.com/geekworks/data-capture/hp8569b.html.  The 3585B program 
builds on and improves the current version of the 8569B program; I'll be 
updating the 8569B program to match as soon as I have time.  (Frank, if you 
want to pick these up for perl examples in the distribution, feel free.)