Tilemap Base Address Register
| Number | $6E |
|---|---|
| Readable | Yes |
| Writable | Yes |
| Short Description | Base address of the 40x32 or 80x32 tile map (similar to text-mode of other computers). |
- 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 map in Bank 5
The value written into bits 5:0 is an offset into 16K bank 5 or 8K bank 7 allowing the tilemap 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 $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).
Default value after soft reset corresponds to the address $6C00, i.e. default value is $2C.