88,89



     1010  FOR CHANGE = DLIST + 6 TO DLIST
           + 204: IF PEEK(CHANGE) = 15 THE
          N POKE CHANGE,14
     1020  IF PEEK (CHANGE) = 79 THEN POKE
          CHANGE,78: NEXT CHANGE
     1030  POKE 87,7:RETURN

     (Actually, 15 ($F) is the DL number for the maximum memory
     mode; it also indicates modes eight through eleven. The DL's for
     these modes are identical.) Fourteen is the ANTIC E mode;
     GR.7.5 This program merely changes GR.8 to mode E in the
     Display List. The value 79 is 64 + 15; mode eight screen with BIT
     6 set for a Load Memory Scan (LMS) instruction (see the DL
     information in locations 560, 561; $230, $231). It does not check
     for other DL bits.

     You can also POKE 87 with the GTIA values (nine to eleven). To
     get a pseudo-text window in GTIA modes, POKE the mode
     number here and then POKE 623 with 64 for mode nine, 128 for
     mode ten, and 192 for mode eleven, then POKE 703 with four, in
     program mode. (In command mode, you will be returned to
     GR.0.) You won't be able to read the text in the window, but you
     will be able to write to it. However, to get a true text window,
     you'll need to use a Display List Interrupt (see COMPUTE!,
     September 1982). If you don't have the GTIA chip, it is still
     possible to simulate those GRAPHICS modes by using DINDEX
     with changes to the Display List Interrupt. See COMPUTE!, July
     1981, for an example of simulating GR.10.

88,89          58,59          SAVMSC
     The lowest address of the screen memory, corresponding to the
     upper left corner of the screen (where the value at this address
     will be displayed). The upper left corner of the text window is
     stored at locations 660, 661 ($294, $295).
     You can verify this for yourself by:

     WINDOW = PEEK(88) + PEEK(89) * 256: POKE WINDOW,33

     This will put the letter "A" in the upper left corner in GR.0, 1 and
     2. In other GRAPHICS modes, it will print a colored block or
     bar. To see this effect, try:

     5   REM FIRST CLEAR SCREEN
     10  GRAPHICS Z: IF Z > 59 THEN END
     15  SCREEN = PEEK (88) + PEEK (89) *
        256
     20  FOR N = 0 TO 255: POKE SCREEN + N
        ,N
     25  NEXT N: FOR N = 1 TO 300: NEXT N: