756



     The blink frequency is set .5 second; to change it, change the
     30 in line 80 to any number from one (1/30 second) to 255 (eight
     .5 seconds). For another way to make the cursor visible or
     invisible, see locations 752 above.

756            2F4            CHBAS
     Character Base Register, shadow for 54281 ($D409). The default
     (initialization value) is 224 ($E0) for uppercase characters and
     numbers; POKE CHBAS with 226 ($E2) to get the lowercase and
     the graphics characters in GR.1 and GR.2. In GR.0 you get the
     entire set displayed to the screen, but in GR.1 and GR.2, you
     must POKE 756 for the appropriate half-set to be displayed.

     How do you create an altered character set? First you must
     reserve an area in memory for your set (512 or 1024 bytes; look at
     location 106; $6A to see how). Then either you move the ROM set
     (or half set, if that's all you intend to change) into that area and
     alter the selected characters, or you fill up the space with bytes
     which make up your own set. Then you POKE 756 with the MSB
     of the location of your set so the computer knows where to find it.

     What does an altered character set look like? Each character is a
     block one byte wide by eight bytes high. You set the bits for the
     points on the screen you wish to be "on" when displayed. Here
     are two examples:

     one byte wide:
     00100000 = 32             #
     00010000 = 16              #
     00010000 = 16              #
     00010000 = 16              #
     00011110 = 30              ####
     00000010 =  2                 #
     00001100 = 12               ##
     00010000 = 16              #

     Hebrew letter Lamed


     one byte wide:
     10000001 = 129          #      #
     10011001 = 153          #  ##  #
     10111101 = 189          # #### #
     11111111 = 255          ########
     11111111 = 255          ########
     10111101 = 189          # #### #
     10011001 = 153          #  ##  #
     10000001 = 129          #      #

     Tie-fighter