Ready-made bytes for plotting one-pixel points in mode 5 (the bottom part of
the split screen). See the dashboard routines SCAN, DIL2 and CPIX2 for
There is one extra row to support the use of CTWOS+1,X indexing in the CPIX2
routine. The extra row is a repeat of the first row, and saves us from having
to work out whether CTWOS+1+X needs to be wrapped around when drawing a
two-pixel dash that crosses from one character block into another. See CPIX2
for more details.