53272

Address 53272 ($D018) is a VIC-II register that generally tells the graphics chip where to "look for graphics", in conjunction with both the text screen and with bitmap graphics.

The text screen

When in text screen mode, the VIC-II looks to 53272 for information on where the character set and text screen character RAM is located:

• The four most significant bits form a 4-bit number in the range 0 thru 15: Multiplied with 1024 this gives the start address for the screen character RAM.
• Bits 1 thru 3 (weights 2 thru 8) form a 3-bit number in the range 0 thru 7: Multiplied with 2048 this gives the start address for the character set.

Bitmap mode

In bitmap mode, 53272 is used to indicate the start address of the bitmap itself, and of the color information to go with the bitmap. Note that with the bitmap in multicolor mode, one of the available colors are always located in the character color RAM, regardless of the contents of 53272.

• The four most significant bits form a 4-bit number in the range 0 thru 15: Multiplied with 1024 this gives the start address for the color information.
• Bit 3 indicates whether the bitmap begins at start address 0/$0 (bit set to "0"), or at 8192/$2000 (bit set to "1").

VIC banks

Notice that all the start addresses of character sets, screen character RAM, bitmaps, and color information, are all relative to the start address of the current VIC bank!.