Memory Paging Control

From SpecNext official Wiki
Revision as of 05:21, 1 December 2019 by Ped7g (talk | contribs) (core 3.0 changes/refresh)
Jump to: navigation, search
Number $7FFD
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 - this is ULA layer shadow, not related to Layer 2 RAM Shadow Page Register ($13)
0-2 Bank number for slot 4 ($C000)

Since core3.0 the Layer 2 can be used together with shadow ULA screen from Bank 7 (previous cores did disable Layer 2).