Difference between revisions of "Memory Paging Control"
From SpecNext official Wiki
m (8 revisions imported) |
|||
| Line 1: | Line 1: | ||
{{Port | {{Port | ||
|Number=$7FFD | |Number=$7FFD | ||
| − | |||
|ShortDesc=Selects active RAM, ROM, and displayed screen. | |ShortDesc=Selects active RAM, ROM, and displayed screen. | ||
|Readable=No | |Readable=No | ||
|Writable=Yes | |Writable=Yes | ||
|Subsystem=Memory map | |Subsystem=Memory map | ||
| + | |PortMask=%01-- ---- ---- --0- | ||
}} | }} | ||
| − | |||
Selects the active memory page in slot 4 at $C000. See [[Memory map]]. | Selects the active memory page in slot 4 at $C000. See [[Memory map]]. | ||
Revision as of 23:04, 19 April 2019
| 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 $5B5C if any OS routines are in use.
| Bit | Effect |
|---|---|
| 6-7 | Undocumented |
| 5 | Lock memory paging (setting to 1 locks pages and cannot be unlocked until next reset) |
| 4 | ROM select (low bit of ROM select on +2/+3) |
| 3 | Shadow Screen toggle
When 1, the "Layer 2" is disabled due to ULA screen being read from other memory bank. For double-buffered ULA screen together with Layer 2 functionality the Timex Sinclair Video Mode Control ($xxFF / 255) is suggested. |
| 0-2 | Bank number for slot 4 ($C000) |