Difference between revisions of "Memory Paging Control"

Revision as of 05:21, 1 December 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 - 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).

@@ Line 20: / Line 20: @@
 | 4 || ROM select (low bit of ROM select on +2/+3)
 |-
-| 3 || Shadow Screen toggle
+| 3 || Shadow Screen toggle - this is ULA layer shadow, not related to {{NextRegNo|$13}}
-When 1, the "Layer 2" is disabled due to ULA screen being read from other memory bank. For double-buffered ULA screen together with Layer 2 functionality the {{PortNo|$xxFF}} is suggested.
 |-
 | 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).