OK the scope can decode some stuff, so it's working at least.
Could this be SIO (Serial Input Output) or SSP (SPI) (Synchronous Serial Port (Serial Peripheral Interface))
On the VFD IC,
Yellow is on p17-SIO chip select input
Red = p15-Serial data output
Blue = p16-Serial clock I/O
Green = p14-Serial data input
So maybe red is some MISO and grn is MOSI ?
As far as I can see, if CH3 is the clock, nothing changes on it's rising edges. But red/grn do change to any state, and seem to start changing exactly when blu starts falling low. There's 8 low points, and 7 high points, but it's pulled high, so that could be 8 highs or 9.
In the link below, their example of SIO, it looks like the data is read on the falling edges of the CLK, so the opposite of mine here.
https://toshiba.semicon-storage.com/us/semiconductor/knowledge/e-learning/village/seven-serial-interfaces-of-toshiba-mcu.htmlIt should be this block diagram in the VFD IC