Difference between revisions of "Memory Paging Control"

From SpecNext official Wiki
Jump to: navigation, search
m (8 revisions imported)
Line 1: Line 1:
 
{{Port
 
{{Port
 
|Number=$7FFD
 
|Number=$7FFD
|PortMask=%01-- ---- ---- --0-
 
 
|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)