Difference between revisions of "Memory Paging Control"

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{{Port
 
{{Port
 
|Number=$7FFD
 
|Number=$7FFD
|PortMask=%01------------0-
+
|PortMask=%01------------0c
 
|ShortDesc=Selects active RAM, ROM, and displayed screen.
 
|ShortDesc=Selects active RAM, ROM, and displayed screen.
 
|Readable=No
 
|Readable=No

Revision as of 15:21, 28 August 2017

Number $7FFD
Decimal
Short desc. Selects active RAM, ROM, and displayed screen.
Bit Mask %01------------0c
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
0-2 Bank number for slot 4 ($C000)