Hi, ngkiller
a couple of years ago, I was build a circuit and soft to drive a 4 backplane display with only the pins of a
processor. The app was based in some documents easily found in www. For example you can try a app
note from NXP, but I thing the used was another from Microchip. Please, check the following :
https://www.nxp.com/docs/en/application-note/AN3412.pdf.
The only requisite, I remember was the configuration of I/O pins should change to out, input, and in
some states leave to float ( tri-state).