collapseos/arch/z80/ti84/blk/602

# Z-Offset

This LCD has a "Z-Offset" parameter, allowing to offset rows on
the screen however we wish. This is handy because it allows us
to scroll more efficiently. Instead of having to copy the LCD
ram around at each linefeed (or instead of having to maintain
an in-memory buffer), we can use this feature.

The Z-Offset goes upwards, with wrapping. For example, if we
have an 8 pixels high line at row 0 and if our offset is 8,
that line will go up 8 pixels, wrapping itself to the bottom of
the screen.

The principle is this: The active line is always the bottom
one. Therefore, when active row is 0, Z is FNTH+1, when row is
1, Z is (FNTH+1)*2, When row is 8, Z is 0.              (cont.)