Dot_ix ($F2C1)

This routine draws a dot at the relative y and relative x position pointed to by the X register. Afterwards, the X register is incremented by 2.

ENTRY:

DP = $D0

X-reg points to the (y,x) coordinate pair

$C828 contains the intensity (Dot_ix only)

EXIT:

X-reg incremented by 2

D-reg trashed

Source