TITLE
Apple III: Console Driver--Screen Mode Switching Program 

Article ID: 23
Created: 9/21/84
Modified: 10/29/84
 

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TOPIC 


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DISCUSSION 

The following program is a demostration of how to change the Apple III screen
mode.

PROGRAM SCREENTEST;

PROCEDURE SCREENMODE (NUMBER: INTEGER);
VAR CH: CHAR;
BEGIN
  IF NUMBER IN [0..2] THEN BEGIN {If the given number is valid}
     WRITE (CHR (14));                {turn off the screen and}
     CH := CHR (16);
     UNITWRITE (1, CH, 1, , 12);    {send the prefix character}
     CH := CHR (NUMBER);
     UNITWRITE (1, CH, 1, , 12);      {and the mode character.}
     IF NUMBER = 2 THEN WRITE (CHR (1));   {If 80 column, restore}
                                           {viewport.}
     WRITE (CHR (28), CHR (15)); {Clear screen and turn it on.}
  END ELSE WRITELN (CHR (7), 'SCREENMODE ERROR '); {else OOPS!}
END;

PROCEDURE TESTERROR;
BEGIN
  WRITE (CHR (28));                         {Clear the screen.}
  GOTOXY (0,11);
  WRITE ('This will generate an error.  ');  {Write some text.}
  SCREENMODE (5);                        {Set an invalid mode.}
  WRITELN;
  WRITE ('Press RETURN to continue: ');
  READLN;
END;

PROCEDURE TEST40;
BEGIN
  SCREENMODE (0);                     {Set 40 column B/W mode.}
  GOTOXY (0,11);
  WRITELN ('This is 40 column text mode.');
  WRITELN;
  WRITE   ('Press RETURN to continue: ');
  READLN;
END;

PROCEDURE TESTCOLOR;
BEGIN
  SCREENMODE (1);                   {Set 40 column color mode.}
  WRITE (CHR (20), CHR (4));    {Set background to Dark Green.}
  WRITE (CHR (28));                         {Clear the screen.}
  WRITE (CHR (19), CHR (13));        {Set forground to Yellow.}
  GOTOXY (0,11);
  WRITELN ('This is 40 column COLOR mode.');
  WRITELN;
  WRITE   ('Press RETURN to quit: ');
  READLN;
END;

BEGIN
  TESTERROR;
  TEST40;
  TESTCOLOR;
  SCREENMODE (2);
END.