Zenith Z-100 Series, Reference Manual, Page: 127 / 163

page 7.38
Video Graphics Programming
If BH is odd, one of the two available palettes is selected by the value in BL.
If BL is 0, the green (I), red (2), yellow (3) palette is selected; if BL is I, the
cyan (I), magenta (2), white (3) palette is selected. The values in parentheses
represent the color numbers used by the graphics calls.
Function Code 12 Write Graphics Pixel
This mode allows you to output a single pixel to a graphics coordinate on the
current screen page. Load DX with a vertical value in the range 0 to 199 and
CX to a horizontal value in the range of 0 to 319 or 0 to 639, depending on
whether 320 x 200 or 640 x 200 video mode has been select ed. Load AL
with the color of the pixel (0 to 3) if in 320 x 200 graphics or (0 to 1) if in
640 x 200 mode.
If the MSB of AL is set, the color value given will be exclusively ORed with the
current color value. This permits simple animation to be implemented.
Function Code 13 Read Graphics Pixel
This operation returns the color of a pixel in a given location, by
returning
the
color value in AL. Before calling, load DX with the vertical position value, and
CX with the horizontal value of the pixeL
Function Code 14 — Dumb Terminal Display
Use of this function allows the user to display information on the monitor as
if it were a simple terminal. Load the character to be written in AL, the foreground
color in BL (for graphics modes), and the display page number in BH.
This routine will check and act upon the backspace (08H), carriage return (ODH),
line feed (OAH), and bell (07H) as commands rather than characters, for screen
formatting.
If a character occurs at the end of a screen line, the cursor is positioned to the
start of the next line.
If a line feed is performed in the last display line on the screen, or if a character
occurs in the last position of this line, the screen will be scrolled up one line.
When scrolling is performed, the attribute for blanked rows in text mode is deter-
mined by the attribute at the cursor position on the previous line, prior to the
scroll.