Difference between revisions of "Tile Definitions Base Address Register"
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|ShortDesc=Base address of the tiles' graphics. | |ShortDesc=Base address of the tiles' graphics. | ||
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| − | : | + | :bit 7 = 1 to select bank 7, 0 to select bank 5 |
| + | :bit 6 = Reserved, must be 0 | ||
:bits 5-0 = MSB of address of the tile definitions in Bank 5 | :bits 5-0 = MSB of address of the tile definitions in Bank 5 | ||
| − | The value written is an offset into | + | The value written into bits 5:0 is an offset into 16K bank 5 or 8K bank 7 allowing the [[Tilemap|tile definitions]] to be placed at any multiple of 256 bytes. The value written here can be thought of as the MSB of an address in bank 5 0x40-0x7f or bank 7 0xc0-0xff. Because bank 7 is only 8K in size, addresses wrap across the 8K boundary instead of the 16K boundary. |
| − | |||
| − | |||
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 $EB the read of this register will produce value $2B (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 $EB the read of this register will produce value $2B (contrary to "reserved" bits in other registers, where read-value should be not assumed by code using it and masking by AND is recommended). | ||
Default value after soft reset corresponds to the address $4C00, i.e. default value is $0C. | Default value after soft reset corresponds to the address $4C00, i.e. default value is $0C. | ||
Latest revision as of 11:44, 3 November 2024
| Number | $6F |
|---|---|
| Readable | Yes |
| Writable | Yes |
| Short Description | Base address of the tiles' graphics. |
- bit 7 = 1 to select bank 7, 0 to select bank 5
- bit 6 = Reserved, must be 0
- bits 5-0 = MSB of address of the tile definitions in Bank 5
The value written into bits 5:0 is an offset into 16K bank 5 or 8K bank 7 allowing the tile definitions to be placed at any multiple of 256 bytes. The value written here can be thought of as the MSB of an address in bank 5 0x40-0x7f or bank 7 0xc0-0xff. Because bank 7 is only 8K in size, addresses wrap across the 8K boundary instead of the 16K boundary.
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 $EB the read of this register will produce value $2B (contrary to "reserved" bits in other registers, where read-value should be not assumed by code using it and masking by AND is recommended).
Default value after soft reset corresponds to the address $4C00, i.e. default value is $0C.