Location of VIC-11 video data in memory (Video Bank selection)

The VIC-II modes can only access a maximum of 16K bytes of memory, out of a total of 64K of potentially available display memory. To select which fourth of the 64K memory will be available for VIC-II video accesses, the user must specify which Video Bank to use. This is done by setting bits 0 and 1 in the Bank Select register (location DD02 hex) as shown.

    Bit Video   Address
    1 0 Bank    Range
    - - ----    --------
    0 0  3      C000-FFFF
    0 1  2      8000-BFFF
    1 0  1      4000-7FFF
    1 1  0         0-3FFF

The same two bits must be set to a 1 in an enable register (location DD00 hex) in order for a 0 data bit to be recognized. Both of these registers, though write only, may have bits shared, elsewhere in the application system. If this is the case, care must be taken to preserve the other port bits not shown, here.

The Video Matrix

The Video Matrix is a block of memory used to store character-organized display data. Depending on whether the chip is in 40 column or 80 column display mode, it is 1024 or 2048 bytes long. Since the VIC-II modes can only access 16K bytes of memory, this means there are 16 or 8 places that the video matrix can appear within the 16K Video Bank, depending on whether 40 or 80 column mode is selected. The location of the Video matrix is chosen by bits 4 through 7 of the Memory Pointers register (address D018 hex). Bit 4 has no effect in 60 column mode.