screen is filled with programmable characters, and you make your changes directly into the memory that the programmable characters get their patterns from.
Each of the locations in screen memory that were used to control what character was displayed, are now used for color information. For example, instead of POKEing a I in location 1024 to make an "A" appear in the top left hand corner of the screen, location 1024 now controls the colors of the bits in that top left space.
Colors of squares in bit map mode do not come from color memory, as they do in the character modes. Instead, colors are taken from screen memory. The upper 4 bits of screen memory become the color of any bit that is set to 1 in the 8 by 8 area controlled by that screen memory location. The lower 4 bits become the color of any bit that is set to a 0.
EXAMPLE: Type the following:
5 BASE=2*4096:POKE53272,PEEK(53272)OR8:REM PUT BIT MAP AT 8192 10 POKE53265,PEEK(53265)OR32:REM ENTER BIT MAP MODENow RUN the program.
Garbage appears on the screen, right? Just like the normal screen mode, you have to clear the HIGH-RESOLUTION (HI-RES) screen before you use it. Unfortunately, printing a CLR won't work in this case. Instead you have to clear out the section of memory that you're using for your programmable characters. Hit the <RUN/STOP> and <RESTORE> keys, then add the following lines to your program to clear the HI-RES screen:
20 FORI=BASETOBASE+7999:POKEI,0:NEXT:REM CLEAR BIT 30 FORI=1024TO2023:POKEI,3:NEXT:REM SET COLOR TO CYAN AND BLACK
Now RUN the program again. You should see the screen clearing, then the greenish blue color, cyan, should cover the whole screen. What we want to do now is to turn the dots on and off on the HI-RES screen.
|This page has been created by Sami Rautiainen.|
|Read the small print.||Last updated May 12, 2002.|