Layer 2 Active RAM Bank Register: Difference between revisions
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|ShortDesc=Sets the [[Memory map|bank]] number where Layer 2 video memory begins. | |ShortDesc=Sets the [[Memory map|bank]] number where Layer 2 video memory begins. | ||
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Bits 5-0 store the number of the "SRAM page" (ie, [[Memory map|bank]]) used for the standard Layer 2 screen. The default is 8. Because the layer 2 screen is 48k, it actually occupies 3 banks, and the number set here is the first; so by default, it occupies banks 8-10. | Bits 5-0 store the number of the "SRAM page" (ie, [[Memory map|bank]]) used for the standard Layer 2 screen. The default is 8. Because the layer 2 screen is 48k, it actually occupies 3 banks, and the number set here is the first; so by default, it occupies banks 8-10. Then later NextZXOS does reconfigure both this and shadow bank to 9 (banks 9-11). | ||
For shadow bank paging see [[Layer_2]] | For shadow bank paging see [[Layer_2]] and {{NextRegNo|$13}}. | ||
Note that this register uses the 16kb bank method, so if you set Nextreg $12,$C if you need to read the contents via 8kb banks you would need to multiply x 2 | Note that this register uses the 16kb bank method, so if you set Nextreg $12,$C if you need to read the contents via 8kb banks you would need to multiply x 2 (16k bank $0C is identical to 8k pages $18 and $19). | ||
Revision as of 01:23, 21 December 2018
| Number | TBRegisterNumber::$12 |
|---|---|
| Readable | TBRegisterReadable::Yes |
| Writable | TBRegisterWritable::Yes |
| Short Description | [[ShortDesc::Sets the bank number where Layer 2 video memory begins.]] |
Bits 5-0 store the number of the "SRAM page" (ie, bank) used for the standard Layer 2 screen. The default is 8. Because the layer 2 screen is 48k, it actually occupies 3 banks, and the number set here is the first; so by default, it occupies banks 8-10. Then later NextZXOS does reconfigure both this and shadow bank to 9 (banks 9-11).
For shadow bank paging see Layer_2 and {{#ask: TBRegisterNumber::$13 }} ($13).
Note that this register uses the 16kb bank method, so if you set Nextreg $12,$C if you need to read the contents via 8kb banks you would need to multiply x 2 (16k bank $0C is identical to 8k pages $18 and $19).