A cartridge system was introduced with the launch of the Plus and GX4000 series. This enabled developers to distribute games via cartridges on the new Amstrad. The cartridges are protected with the ACID chip.
All known manufactured cartridges contain EPROMs (rather than PROMs or ROMs). The cartridges can be fitted with different EPROMs in range of 32kb through 512kb, but only 128kb to 256kb versions are known to have been produced. The cartridge PCBs typically include six LK Links to match the PCB to the EPROM pin-outs:
VCC ---LK1--- EPROM.A18 ---LK2--- CA18 VCC ---LK3--- EPROM.A17 ---LK4--- CA17 VCC ---LK5--- EPROM.A15 ---LK6--- CA15
Usually the following LKs should be installed:
(----- EPROM -----) (------------------------ Links installed -------------------------) Type Pins Size A15 A17 A18 27C256 28 32K LK5 (A15=VCC=High) LK3 (A17=VCC=Supply) N/A 27C512 28 64K LK6 (A15=A15=Address) LK3 (A17=VCC=Supply) N/A 27C1001 32 128K LK6 (A15=A15=Address) N/A LK1 (A18=VCC=/PGM) 27C2001 32 256K LK6 (A15=A15=Address) LK4 (A17=A17=Address) LK1 (A18=VCC=/PGM) 27C4001 32 512K LK6 (A15=A15=Address) LK4 (A17=A17=Address) LK2 (A18=A18=Address)
Some cartridge PCBs don't have any LKs installed, instead, the etched circuit has hardwired connections between some of them. One could scratch them off, and then use the LK soldering points to reconfigure the board for eproms of other size.
The EPROMs aren't encrypted, making it very easy to dump their content, or to replace them by other EPROMs. However, all cartridges must contain an ACID chip, otherwise the Plus/GX4000 refuses to work, meaning that unlicensed third-party developers couldn't produce cartridges without buying the ACID hardware from Amstrad.
Amstrad released a Demonstration system for his retailer in order to show GX4000 games: the Amstrad CSD (Cartridge Software Demonstrator).
It was a 464 Plus motherboard, with an extra "daughter board" allowing the insertion of 12 games cartridges, plus an extra special cartridge acting as an OS.
Courtesy of Amstrad.cpc.free.fr
More informations at the Amstrad CSD page.