This equipment is said to output PCL3 or PCL5 data direct to a HP printer. However, the PDFs mainly failed to be correctly generated by the Retro-Printer Module, which lead to some head scratching as GhostPCL which does the heavy conversion work for HP printer data handles both PCL3 and PCL5.
Once the customer sent through the contents of their /home/pi/data directory, we could see that the captured data looked nothing like PCL3 or PCL5 which was surprising.
Thankfully, we could quickly analyse the data using a Sinclair QL emulator running under Windows (!) and realised that bit 8 in every character was set - adding 128 to every character. We therefore realised that the solution was to change the configuration of the bit_depth setting on the Retro-Printer to 7 and this resolves the issue.
Phew !!
This is only the second piece of equipment where we have found that the 8th bit was always high for some reason - the other piece of equipment was designed for a Siemens printer.
Did HP printers allow you to set the bit depth in the past?