Display Address Translator (DAT)

The C4567R6 contains a special piece of hardware, known as the Display Address Translator, or DAT, which allows the programmer to access, the bitplanes directly. In the old VIC configuration, the bitmap was organized as 25 rows of 40 stacks of 8 sequential bytes. This is great for displaying 8 x 8 characters, but difficult for displaying graphics.

The DAT overcomes the original burden by allowing the programmer to specify the (X,Y) location of the byte of bitplane memory to be read, modified, or written. This is done by writing the (X,Y) coordinates to the BPX and BPY register, respectively. The user can then read, modify, or write the specified location by reading, modifying, or writing one of the eight Bitplane registers. There is one bitplane register for each bitplane.

The DAT automatically determines whether to use 320 or.640 pixel mode, and whether to use 200 or 400 line mode. It will also use the areas specified ir the bitplanes, using the Bitplane Address registers.

Horizontal and Vertical Positioning

The C4567R6 has two registers to allow the programmer to alter the positioning of the display relative to the borders of his CRT (television or monitor). Initially the positioning registers are set to zero, to give C64 standard positioning. These registers are signed, two's complement values which specify an offset from the default positions.

Chroma Killer

The C4567R6 provides analog RGB video, with sync on all colors, an analog luminance output, with sync, and an analog NTSC (or PAL on PAL versions) chrominance output. It also provides a separate digital video signal, and a separate digital sync. When using the C4567R6 with a black and white television receiver , it may be best to suppress the chrominance information. This can be done by setting the MONO bit in control register "B".

Additional ROM

The C4567R6 does all decoding for ROMs. It supports a total of 32K of ROM, which is 12K over what the C64 is configured for. This 12K of extra ROM is available in one 8K block at 8000 (hex), and one 4K block at C000 (hex). To enable ROM at these areas, set the ROM@8000 or ROM@C000 bits in Control Register "A". (Note that there are other chips in the C65 which extend this addressing limitation. The C65 has a 1MB ROM built-in.)

Alternate Character Set

Ordinarily, the C4567R6 will always fetch ROM-based character data from addresses DOOO-DFFF. If the CROM@9000 bit is set in control register "A", ROM-based character data will be fetched from addresses 9000-9FFF. This allows for an alternate ROM-based character set.