Apple IIe - Page 306

306 Apple lie Users Handbook
This subroutine also writes a ten second leader and computes a
checksum.
Monitor Subroutines -- Graphics
The monitor contains subroutines that can be used to manipu-
late the graphics display.
CLRSCR (($F832/63538) A=?? X = -- Y = ??
CLRSCR clears all 48 lines of the low resolution graphics screen
to black.
CLRTOP ($F836/63542) A=?? X = -- Y = ??
CLRTOP clears the low resolution graphics display. However ,
CLRTOP
only clears the top 40 lines.
HLINE ($F819/63513) A=?? X = -- Y = ??
HLINE plots a horizontal string of pixels of the color set by
SETCOL
or NEXTCOL. HLINE is used only with a low resolution
display. Prior to calling HLINE, the accumulator must be loaded
with the vertical coordinate; the Y-register must be loaded with
the leftmost horizontal coordinate ; and memory location $2C
must be
loaded with the rightmost horizontal coordinate.
NEXTCOL ($F85F/63583) A= -- X = -- Y = --
NEXTCOL adds 3 to the current low resolution color.
PLOT ($F800/63488) A = ? ? X = -- Y = --
PLOT sets a certain pixel of the low resolution screen to the color
last selected by SETCOL or NEXTCOL. The vertical position is
loaded into the accumulator. The horizonal position is loaded in
the Y-register.