Difference between revisions of "Tilemap Base Address Register"

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:bits 5-0 = MSB of address of the tilemap in Bank 5
 
:bits 5-0 = MSB of address of the tilemap in Bank 5
  
The value written is an offset into Bank 5 allowing the tilemap to be placed at any multiple of 256 bytes.
+
The value written is an offset into Bank 5 allowing the [[Tilemap|tilemap]] to be placed at any multiple of 256 bytes.
  
 
Writing a physical MSB address as $40-$7F or $C0-$FF range is permitted (the top bits will be ignored).
 
Writing a physical MSB address as $40-$7F or $C0-$FF range is permitted (the top bits will be ignored).
  
 
The value read back may be treated as a full 8-bit value (with the top two bits equal to zero), i.e. upon writing value $45 the read of this register will produce value $05 (contrary to "reserved" bits in other registers, where read-value should be not assumed by code using it and masking by AND is recommended).
 
The value read back may be treated as a full 8-bit value (with the top two bits equal to zero), i.e. upon writing value $45 the read of this register will produce value $05 (contrary to "reserved" bits in other registers, where read-value should be not assumed by code using it and masking by AND is recommended).

Revision as of 05:49, 23 May 2019

Number $6E
Readable Yes
Writable Yes
Short Description Base address of the 40x32 or 80x32 tile map (similar to text-mode of other computers).
bits 7-6 = Read back as zero, write values ignored
bits 5-0 = MSB of address of the tilemap in Bank 5

The value written is an offset into Bank 5 allowing the tilemap to be placed at any multiple of 256 bytes.

Writing a physical MSB address as $40-$7F or $C0-$FF range is permitted (the top bits will be ignored).

The value read back may be treated as a full 8-bit value (with the top two bits equal to zero), i.e. upon writing value $45 the read of this register will produce value $05 (contrary to "reserved" bits in other registers, where read-value should be not assumed by code using it and masking by AND is recommended).