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System Specification for C65Fred BowenMarch 1, 1991

80 Column (character) or 640 Pixel (bitmap or bitplane) Mode

You can put the C4567R6 into "80 Column Mode" or "640 horizontal pixel mode by setting the H640 bit in control register "B". The normal: horizontal rendering is 40 columns or 320 pixels.

In 80 column character mode, several things change. The Video Matrix becomes 2K bytes long, where it used to be IK in 40 column mode. The character color RAM also becomes 2K bytes long. The locations of these areas do not change from the prior convention, except that the low order video matrix address bit is not used in 80 column mode. where the programmer used to have 16 choices for locating the Video Matrix within a video bank, in 80 column mode there are only 8 choices.

Although the color RAM doubles in size to 2K bytes, the area provided for color RAM in the 1/0 map only allows for 1K of color RAM.-To read or write the second 1K of color RAM requires that you move CIA1, CIA2, I/O1, and I/O2 out of the way. To do this, set the "COLOR RAM @DC00" bit in Control Register "A".

In 640 pixel bitmap mode, similar changes occur. The video matrix and color RAM double in size and are positioned in the memory map exactly as is done in 80 column character mode. The bitmap must now also double in size from 8K to 16K bytes. Because the total memory that the video matrix and the bitmap would require now exceeds the normal 16K byte video bank size, the video bank size has been doubled from 16K to 32K for the bitmap only. The least significant video bank bit is ignored, and the high order character generator bank bit selects which half of the 32K video bank that bitmaps will be fetched from. The video matrix is still fetched from the normal 16K video bank.

In 80 column or 640 pixel mode, the sprite pointers are at the end of the 2K byte video matrix, where they used to be at the end of the 1K byte video matrix, in 40 column or 320 pixel mode. The size, location, and resolution of sprites are not affected by any of the mode switches.



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Read the small print. Last updated March 24, 2003.