Vertical scroll register ($FF9C) is not implemented.

[ejaquay]

From Lomont: "The vertical scroll register is used to allow smooth scrolling in text modes. Consecutive numbers scroll the screen upwards one scan line at a time in video modes where more than one scan line makes up a row of text (typically 8 lines per character row) or graphics (double height + graphics)."

tcc1014registers.cpp GimeWrite() ignores the register.

[ejaquay]

There is also a disputed report that FF9C does not work properly on Mame.

[ejaquay]

Vertical scroll is reported to work properly on Xroar and there is a test program on disk VSC.DSK. Mentioned on discord assembler channel.