HP7475 Plotter with HP48

[Hiwi]

Hi,
i have recently purchased a HP7475- OPT 001 Plotter with serial interface for little money. The plotter did not work, the power supply was short-circuited but this was easy to fix, because it is simple linear regulated circuit with standard parts.

The pen carussel was not moving, There is a plastic connection rod on the stepper motor which broke in thousand pieces. The material became brittle over years.

I made a new one with my CNC milling machine of fiberglass plastic. May be there is a better solution with a 3D printer.

At least the plotter came back to life.

I was inspired from a video back to 2018 on a HP calculator conference, where it was demonstrated connected to a HP48!

This was working out of the box, but only with simple instructions until buffer overrun! (up to 1024 Bytes)
In the manual there are examples for implementation a softwarebase handshaking.
This could be easily made, because you can poll the free buffer size or let the plotter send a free configurable character if the buffer gets full (at any size!)

But the HP48 supports XON/OFF protocol, so it should be possible to get it working with larger plotter file. The trick is to configure the plotter to use XON/XOFF protocol.
This works with ESC.N;19: and ESC.I81;;17:

I was now able to send e.g. the 25kB columbia HPGL file without any problems.

Ralf