[[Image:Inside GX4000 cart 1.jpg|frame|right|ACID protection chip within a cartridge (bottom)]]
The '''ACID''' ('''A'''mstrad '''C'''artridge '''I'''dentification '''D'''eviceAmstrad Cartridge Identification Device) protection chip is used in the [[GX4000 cartridge|cartridges]] of the [[Plus]] series and the [[GX4000]] game console. It is labeled with "Amstrad 40908". Because this chip was a custom creation by Amstrad it is currently not possible to replace this chip nor to build new cartridges, because it is not known how it works.
if PinCCLR=0 then ShiftReg=1FFFFh ;\done at falling CLK edge
PinSIN=ShiftRegBit0 ;/
Replacing or overwriting the EPROM in cartridges is easy, so the ACID doesn't prevent piracy or homebrew programming. However, it does prevent commercial developers from producing unlicensed cartridges.
== Pinout ==