Memory Paging Control - Revision history

Johnnyo: add the 1FFD reference

2026-02-22T23:01:25Z

add the 1FFD reference

← Older revision		Revision as of 00:01, 23 February 2026
Line 19:		Line 19:
	\| 5 \|\| Lock memory paging (setting to 1 locks pages and cannot be unlocked until next reset (on regular ZX128))		\| 5 \|\| Lock memory paging (setting to 1 locks pages and cannot be unlocked until next reset (on regular ZX128))
	\|-		\|-
	\| 4 \|\| ROM select (0 = 128k editor, 1 = 48k basic) (low bit of ROM select on +2/+3)		\| 4 \|\| ROM select (0 = 128k editor, 1 = 48k basic) (low bit of ROM select on +2/+3, see {{PortNo\|$1FFD}})
	\|-		\|-
	\| 3 \|\| Shadow Screen toggle (0 = bank 5, 1 = bank 7) - this is ULA layer shadow, not related to {{NextRegNo\|$13}}		\| 3 \|\| Shadow Screen toggle (0 = bank 5, 1 = bank 7) - this is ULA layer shadow, not related to {{NextRegNo\|$13}}

2026-02-22T22:52:38Z

fix the reg link

← Older revision		Revision as of 23:52, 22 February 2026
Line 15:		Line 15:
	! Bit !! Effect		! Bit !! Effect
	\|-		\|-
	\| 6-7 \|\| Extra two bits for 16K RAM bank if in Pentagon 512K / 1024K mode (see {{PortNo\|$DFFD}}, {{NextRegNo\|$8f}})		\| 6-7 \|\| Extra two bits for 16K RAM bank if in Pentagon 512K / 1024K mode (see {{PortNo\|$DFFD}}, {{NextRegNo\|$8F}})
	\|-		\|-
	\| 5 \|\| Lock memory paging (setting to 1 locks pages and cannot be unlocked until next reset (on regular ZX128))		\| 5 \|\| Lock memory paging (setting to 1 locks pages and cannot be unlocked until next reset (on regular ZX128))

2024-11-03T13:03:33Z

updated to 78a6ee50

← Older revision		Revision as of 14:03, 3 November 2024
Line 15:		Line 15:
	! Bit !! Effect		! Bit !! Effect
	\|-		\|-
	\| 6-7 \|\| Extra two bits for 16K RAM bank if in Pentagon 512K mode (see {{PortNo\|$DFFD}})		\| 6-7 \|\| Extra two bits for 16K RAM bank if in Pentagon 512K / 1024K mode (see {{PortNo\|$DFFD}}, {{NextRegNo\|$8f}})
	\|-		\|-
	\| 5 \|\| Lock memory paging (setting to 1 locks pages and cannot be unlocked until next reset (on regular ZX128))		\| 5 \|\| Lock memory paging (setting to 1 locks pages and cannot be unlocked until next reset (on regular ZX128))

2020-05-04T11:45:02Z

← Older revision		Revision as of 12:45, 4 May 2020
Line 1:		Line 1:
	{{Port		{{Port
	\|Number=$7FFD		\|Number=$7FFD
			\|NumberDec=32765
			\|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]] (soft reset = 0).		Selects the active memory page in slot 4 at $C000. See [[Memory map]] (soft reset = 0).

2020-04-16T00:43:39Z

core 3.1.4 changes/refresh

← Older revision		Revision as of 01:43, 16 April 2020
Line 7:		Line 7:
	\|PortMask=%01-- ---- ---- --0-		\|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]] (soft reset = 0).

	Any values written to this port should also be stored at $5B5C if any OS routines are in use.		Any values written to this port should also be stored at $5B5C if any OS routines are in use.
Line 14:		Line 14:
	! Bit !! Effect		! Bit !! Effect
	\|-		\|-
	\| 6-7 \|\| ~~Undocumented~~		\| 6-7 \|\| Extra two bits for 16K RAM bank if in Pentagon 512K mode (see {{PortNo\|$DFFD}})
	\|-		\|-
	\| 5 \|\| Lock memory paging (setting to 1 locks pages and cannot be unlocked until next reset (on regular ZX128))		\| 5 \|\| Lock memory paging (setting to 1 locks pages and cannot be unlocked until next reset (on regular ZX128))

2020-01-07T17:37:19Z

adding info

← Older revision		Revision as of 18:37, 7 January 2020
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	When the port is locked (bit 5), the shadow screen toggle is considered part of the paging, i.e. it's not possible to flip between shadow and regular screen. Except for {{NextRegNo\|$69}} which works even when port is locked, and you can unlock the port back (without reset) with {{NextRegNo\|$08}}.		When the port is locked (bit 5), the shadow screen toggle is considered part of the paging, i.e. it's not possible to flip between shadow and regular screen. Except for {{NextRegNo\|$69}} which works even when port is locked, and you can unlock the port back (without reset) with {{NextRegNo\|$08}}.

			ULA shadow screen from Bank 7 has higher priority than Timex modes, setting bit 3 to "1" when in one of the extended Timex graphic modes will switch to classic ZX128 ULA mode using Bank 7 data.

2019-12-31T10:14:15Z

adding info

← Older revision		Revision as of 11:14, 31 December 2019
Line 18:		Line 18:
	\| 5 \|\| Lock memory paging (setting to 1 locks pages and cannot be unlocked until next reset (on regular ZX128))		\| 5 \|\| Lock memory paging (setting to 1 locks pages and cannot be unlocked until next reset (on regular ZX128))
	\|-		\|-
	\| 4 \|\| ROM select (low bit of ROM select on +2/+3)		\| 4 \|\| ROM select (0 = 128k editor, 1 = 48k basic) (low bit of ROM select on +2/+3)
	\|-		\|-
	\| 3 \|\| Shadow Screen toggle - this is ULA layer shadow, not related to {{NextRegNo\|$13}}		\| 3 \|\| Shadow Screen toggle (0 = bank 5, 1 = bank 7) - this is ULA layer shadow, not related to {{NextRegNo\|$13}}
	\|-		\|-
	\| 0-2 \|\| Bank number for slot 4 ($C000)		\| 0-2 \|\| Bank number for slot 4 ($C000)

2019-12-02T20:14:18Z

core 3.0 changes/refresh

← Older revision		Revision as of 21:14, 2 December 2019
Line 16:		Line 16:
	\| 6-7 \|\| Undocumented		\| 6-7 \|\| Undocumented
	\|-		\|-
	\| 5 \|\| Lock memory paging (setting to 1 locks pages and cannot be unlocked until next reset)		\| 5 \|\| Lock memory paging (setting to 1 locks pages and cannot be unlocked until next reset (on regular ZX128))
	\|-		\|-
	\| 4 \|\| ROM select (low bit of ROM select on +2/+3)		\| 4 \|\| ROM select (low bit of ROM select on +2/+3)
Line 26:		Line 26:

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

			When the port is locked (bit 5), the shadow screen toggle is considered part of the paging, i.e. it's not possible to flip between shadow and regular screen. Except for {{NextRegNo\|$69}} which works even when port is locked, and you can unlock the port back (without reset) with {{NextRegNo\|$08}}.

2019-12-01T05:21:09Z

core 3.0 changes/refresh

← Older revision		Revision as of 06:21, 1 December 2019
Line 20:		Line 20:
	\| 4 \|\| ROM select (low bit of ROM select on +2/+3)		\| 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 ($C000)		\| 0-2 \|\| Bank number for slot 4 ($C000)
	\|}		\|}

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

2019-04-19T23:04:30Z

← Older revision		Revision as of 00:04, 20 April 2019
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]].