GPIB Interface for PM3365A Oscilloscope

The Philips PM3365A oscilloscope I inherited last year works fine – but it has one drawback: the only way to export data is via a GPIB interface. I had the opportunity to borrow a Prologix GPIB interface to test what can be done with this interface – it turns out remote control of the oscilloscope is possible, but not really useful. However, with the GPIB interface in listen mode, the scope is able to generate screenshots by pressing the “plot” button on the front panel.

I recently found and decided to build one:

GPIB Interface photo 1

(Don’t ask where I got that GPIB-to-IDC cable – it was salvaged from some old HP equipment many years ago, waiting in storage for just this occasion).

GPIB Interface photo 2

GPIB Interface photo 3

Front- and backplates were later milled from FR-4 and painted black – not much to photograph after mounting them 😉

Since I wanted to use Prologix-compatible commands, I started by using the firmware from, patched in the I/O definitions from the Nano3 version and added a quick-hack to add listen-only mode. By setting the GPIB address to 5 and default mode to listener, the adapter starts spewing out plot data on the serial port as soon as I press the plot button on the oscilloscope without requiring any manual configuration.

I currently use a quick-hack script to capture that data to a file without a terminal program’s capture function: save-plot

The PM3365A supports multiple printers/plotters. The best option for post-processing seems to be HP7550 – there is a tool called hp2xx that converts HPGL files to bitmap, but the result leaves room for improvement: the grid is plotted last, obscuring the traces – however, since the oscilloscope uses separate plotter pens for the grid and the 4 traces (2 input channels + 2 reference memory), this can be fixed by generating separate bitmaps and merging them using ImageMagick: convert-plot

The result looks good:

Much better than taking screenshots with a camera!

(firmware sources withheld until license of original firmware can be verified).

2017-11-05 by rincewind