&os9level; allows the VDG display to be used in alphanumeric, semigraphic, and graphics modes. There are many built-in functions to control the display, which are activated by used of various ASCII control character. Thus, these functions are available for use by software written in any language using standard output statements (such as "PRINT" in BASIC). The &make;'s Basic09 language has a Graphics Interface Module that can automatically generate these codes using Basic09 RUN statements. The display system has two display modes: Alphanumeric ("Alpha") mode and Graphics mode. The Alphanumeric mode also includes "semigraphic" box-graphics. The &make;'s display system uses a separate - memory area for each display mode so operations on the Alpha display do not affect the Graphics display, and visa-versa. Either display can be selected under software control. 8-bit characters sent to the display system are interpreted according to their numerical value, as shown in the chart below. Character Range (Hex) Mode/Used For 00 - 0E Alpha Mode - cursor and screen control 0F - 1B Graphics Mode - drawing and screen control 1C - 20 Not used 20 - SF Alpha Mode - upper case characters 60 - 7F Alpha Mode - lower case characters 80 - FF Alpha Mode - Semigraphic patterns The graphics and alphanumeric functions are handled by the OS-9 device driver module called "CCIO".

This is the "standard" operational mode. It is used to display alphanumeric characters and semigraphic box graphics, and simulates the operation of a typical computer terminal with functions for scrolling, cursor positioning, clear screen, line delete, etc. Each 8-bit character is assumed to be an ASCII character and is displayed if its high order bit (sign bit) is cleared. Lower case letters are displayed in reverse video. If the high order bit of the character is set it is assumed to be a "Semigraphic 6" graphics box. See the &make; manual for an explanation of semigraphics functions. Control Code Name/Function 01 HOME - return cursor to upper left hand corner of screen 02 CURSOR XY - move cursor to character X of line Y. The binary value minus 32 of the two characters following the control character are used as the X and Y coordinates. For example, to position the cursor at character 5 of line 10, you must give X=37 and Y42 03 ERASE LINE - erases all characters on the cursor's line. 06 CURSOR RIGHT - move cursor right one character position 08 CURSOR LEFT - move cursor left one character position 09 CURSOR UP - move cursor up one line 10 CURSOR DOWN (linefeed) move cursor down one line 12 CLEAR SCREEN - erase entire screen and home cursor 13 RETURN - return cursor to leftmost character of line 14 DISPLAY ALPHA - switch screen from graphic mode to alpha numeric mode

This mode is used to display high-resolution 2- or 4-color graphics, and it includes commands to: set color; plot and erase individual points; draw and erase lines; position the graphics cursor; and draw circles. The DISPLAY GRAPHICS command must be executed before any other graphics mode command is used. It causes the graphics screen to be displayed and sets a current display format and color. The Li.u.t time the DISPLAY GRAPHICS command is given, a 6144 byte display memory is allocated by OS-9, so there must be at least this much continuous free memory available (the OS-9 "MFREE" command can be used to check free memory). This memory is retained until the END GRAPHICS command is given, even if the program that initiated Graphics mode finishes, so it important that the END GRAPHICS command be used to give up the display memory when Graphics mode is no longer needed. Graphics mode supports two basic formats: Two-Color which has 256 horizontal by 192 vertical points (G6R mode); and Four Color which has 128 horizontal by 192 vertical points (G6C mode). Two color sets are available in either mode. Regardless of the resolution of the format selected, all Graphics mode commands use a 256 by 192 point coordinate system. The X and Y coordinates are always positive numbers which assume that point 0,0 is the lower lefthand corner of the screen. An invisible Graphics Cursor is used by many command to reduce the amount of output required to generate graphics. This cursor can be explicitly set to any point using the SET GRAPHICS CURSOR command. Also, all other commands that include X,Y coordinates (such as SET POINT) move the graphics cursor to the specified position. Code Format 00 256 x 192 two-color graphics 01 128 x 192 four-color graphics Two Color Format Four Color Format Char Background Foreground Background Foreground Color Set 1 00 Black Black Green Green 01 Black Green Green Yellow 02 Green Blue 03 Green Red Color Set 2 04 Black Black Buff Buff 05 Black Buff Buff Cyan 06 Buff Magenta 07 Buff Orange Color Set 3* 08 Black Black 09 Black Dark Green 10 Black Med. Green 11 Black Light Green Color Set 4* 12 Black Black 13 Black Green 14 Black Red 15 Black Buff * Color sets 3 and 4 not available on PAL video system (European) models. These color sets work only with NTSC (U.S., Canada, Japan) models. Control Code Name/Function 15 DISPLAY GRAPHICS - switches screen to graphics mode. This command must be given before any other graphics commands are used. The first time this command is given, a 6K byte display buffer is assigned. If 6K of contiguous memory is not available an error is returned. This command is followed by two characters which specify the graphics mode and current color/color set, respectively. 16 PRESET SCREEN - presets entire screen to color code passed in next character. 17 SET COLOR - selects foreground color (and color set) passed in next character, but does not change graphics mode. 18 QUIT GRAPHICS - disables graphics mode and returns the 6K byte graphics memory area to OS-9 for other use, and switches to alpha mode. 19 ERASE GRAPHICS - erases all points to background color and homes graphics cursor to the desired position. 20 HOME GRAPHICS CURSOR - moves graphics cursor to coordinates 0,0 (lower left hand corner). 21 SET GRAPHICS CURSOR - moves graphics cursor to given coordinates X,Y. The binary value of the two characters that immediately follow are used as the X and Y values, respectively. 22 DRAW LINE - draws a line of the current foreground color from the current graphics cursor position to the given X,Y coordinates. The binary value of the two characters that immediately follow are used as the X and Y values, respectively. The graphics cursor is moved to the end point of the line. 23 ERASE LINE - same as DRAW LINE except the line is "drawn" in the current background color, thus erasing the line. 24 SET POINT - sets the pixel-at point X,Y to the current foreground color. The binary value of the two characters that immediately follow are used as the x and Y values, respectively. The graphics cursor is moved to the point Set. 25 ERASE POINT - same as DRAW POINT except the point is "drawn" in the current background color, thus erasing the point. 26 DRAW CIRCLE - draws a circle of the current foreground color with its center at the current graphics cursor position using a radius R which is obtained using the binary value of the next character. The graphics cursor position is not affected by this command.

The &make; I/O driver includes OS-9 Get Status commands that return the display status and joystick values, respectively. These are accessable via the Basic09 Graphics Interface Module, or by the assembly language system calls listed below: GET DISPLAY STATUS: Calling Format lda #1 (path number) ldb #SS.DStat (Getstat code $12) os9 I$GSTT call OS-9 Passed nothing Returns X = address of graphics display memory Y = graphics cursor address x=MSB y =LSB A = color code of pixel at cursor address GET JOYSTICK VALUES: Calling Format lda #1 (path number) ldb #SS.Joy (Getstat code $13) os9 I$GSTT call OS-9 Passed X = 0 for right joystick; 1 for left joystick Returns X = selected joystick x value (0-63) Y = selected joystick y value (0-63) A = $FF if fire button on; $00 if off 1st Byte 2nd Byte 3rd Byte Function 00 Null 01 Home Alpha Cursor 02 Column+32 Row+32 Position Alpha Cursor 03 Erase Line 06 Cursor Right 08 Cursor Left 09 Cursor Up 10 Cursor Down 12 Clear Screen 13 Carriage Return 14 Select Alpha Mode 15 Mode Color Code Select Graphics Mode 16 Color Code Preset Screen 17 Color Code Select Color 18 Quit Graphics Mode 19 Erase Screen 20 Home Graphics Cursor 21 X Coord Y Coord Move Graphics Cursor 22 X Coord Y Coord Draw Line to X/Y 23 X Coord Y Coord Erase Line to X/Y 24 X Coord Y Coord Set Point at X/Y 25 X Coord Y Coord Clear Point at X/Y 26 Radius Draw Circle