I've rewritten my old sequencer code to accomodate changes to the circuit design. Some of the display pins were shifted around. In the process, I discovered that the circuit was set to use 8px wide fonts while my software uses 6px fonts. To fix this I've modified the cable between the controller and display. I've also added a jumper to version 1.2 of the controller hardware, making it possible to switch between 6 and 8 pixel wide fonts.
I had to add a 1us delay to the data output functions too, to prevent 'lost bytes' when writing to the display.