Memory Paging Control: Difference between revisions
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| 3 || Shadow Screen toggle | | 3 || Shadow Screen toggle | ||
When 1, the "Layer 2" is disabled due to ULA screen being read from other memory bank. For double-buffered ULA screen together with Layer 2 functionality the {{PortNo|$xxFF}} is suggested. | |||
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| 0-2 || Bank number for slot 4 ($C000) | | 0-2 || Bank number for slot 4 ($C000) | ||
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Revision as of 19:29, 21 December 2018
| Port Number | $7FFD |
|---|---|
| Decimal | |
| Short desc. | Selects active RAM, ROM, and displayed screen. |
| Bit Mask | %01-- ---- ---- --0- |
| Readable | No |
| Writable | Yes |
| Subsystem | Memory map |
Selects the active memory page in slot 4 at $C000. See Memory map.
Any values written to this port should also be stored at $5B5C if any OS routines are in use.
| Bit | Effect |
|---|---|
| 6-7 | Undocumented |
| 5 | Lock memory paging (setting to 1 locks pages and cannot be unlocked until next reset) |
| 4 | ROM select (low bit of ROM select on +2/+3) |
| 3 | Shadow Screen toggle
When 1, the "Layer 2" is disabled due to ULA screen being read from other memory bank. For double-buffered ULA screen together with Layer 2 functionality the NextPort:$xxFF is suggested. |
| 0-2 | Bank number for slot 4 ($C000) |