Memory Paging Control

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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

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)