Internal 512 KB RAM expansion for CPC6128 from german magazine c't, issue 10/1987. The DIY project name is CPC 6512.
One half (256K) of the total (512K) expansion memory can be accessed as Video RAM (with normal expansions, only 64 KB are accessible as Video RAM). The c't expansion is compatible with Standard Memory Expansions, and provides the additional CRTC feature, but it misses 64 KB usually addressed via I/O ports &7FFC, &7FFD, &7FFE and &7FFF.
One issue later, c't 11/1987, the magazine published a driver which creates a RAM disk within the additional memory. This RAM disk can be used in AMSDOS.
Technical
I/O Ports are &7FC4, &7FC5...&7FF7. &7FC0 selects the first 64 KB. With this expansion the CPC can access 512 KB RAM total. With a "normal" 512 KB it can access 576 KB (64 KB + 512 KB).
Scanned Article / Schematics
c't, issue 10/1987 (RAM schematic)
c't, issue 11/1987 (RAM disc driver)
Offtopic
The CPC 6512 c't Memory Expansion is not to be confused with issues CPC 6512 and CPC 6513 of the more popular World War II Fanzine from Concord Publications Company.
CPC 6512
CPC 6513
