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Download BBC Microcomputer Advanced User Guide
Transcript
&C447—&C458 contain various VDU section control numbers, of no direct relation to any screen parameters. Note that this zone overlaps the previous table. &C459—&C45D contain one byte per memory map type (see above) giving the most significant byte of the number of bytes taken up by the screen. The least significant byte is always zero. &C45E—&C462 contain one byte per memory map type (see above) giving the most significant byte of the address of the first location used by the screen. The least significant byte is always zero. &C463—&C46D contain tables used by the VDU section to index into the other tables. &C46E—&C4A9 contain tables of values to be sent to the various 6845 registers. There is one block of 12 bytes for each of the five memory map types (see above). &C46E—&C479 6845 registers 0-11 for memory map type 0 (modes 0-2). &C47A—&C485 6845 registers 0-11 for memory map type 1 (mode 3). &C486—&C491 6845 registers 0-11 for memory map type 2 (modes 4-5). &C492—&C49D 6845 registers 0-11 for memory map type 3 (mode 6). &C49E—&C4A9 6845 registers 0-11 for memory map type 4 (mode 7). &C4AA—&C4B5 are used by the VDU driver as Jump table addresses into its internal plotting routines. They should not be used by the user at all. 285
