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A quick addendum to the HSYNC/VSYNC used in the P2:

helwie44 measured them off his P2U using a port extender and logic analyser:





He writes: "Here is the original 15.15 kHz HSYNC to the 8085, i.e. there's an interrupt from the CRT to the CPU every 66µs. But in reality those interrupts are being processed only when needed on the P2 - a mask opens the RST55 e.g. in case a scroll is needed".

He's outlined the mechanism in handwritten notes which I've uploaded here and on the FTP.