ACID Verilog code

 

Nilquader and I decided to release our Verilog code (based on Nocash’s decryption of the algorithm) to “emulate” the ACID protection chip of the Amstrad Plus. So, you can now find it here (for more information have a look at the ACID article of the CPCWiki):

Selec All Code:
1
 

But this isn’t everything about the ACID. We also found a timing problem during the investigation with a logic analyzer, which you can see here:

ACID initialisation by Grim

ACID initialisation (by Grim)

You will find glitches on the /CCLR line which show that the SIN contact should be changed… All in all it is possible to use a fast flip-flop to change the SIN signal when such a glitch occurs (see picture below).

Flip flop for ACID replacement

Flip flop for ACID replacement

You see, this is a very simple schematic, but it isn’t much cheaper than a CPLD, which emulates the full ACID and it comes with a disadvantage: it won’t work with a reset, so you always have to switch the CPC off and on again.

So, have fun with it :-).

 

  2 Responses to “ACID Verilog code”

  1. […] or the Symbiface II) and we are also able to produce new cartridges for the Amstrad Plus since the ACID chip was reverse engineered, but we are missing more ROM games. You can read more about the competition (e.g. the rules, the […]

  2. […] After years of inactivity I decided to release two old project, which I started to work on in 2010, publicly on my GitHub account. I have not produced any prototypes yet, so they are currently more a draft. Both projects use a flash EPROM to store the data in the cartridge. The first one is a simple Amstrad Plus / Amstrad GX4000 cartridge, which can be equipped with an original ACID protection chip or with a Xilinx XC9536 CPLD for ACID emulation (you can read more about the emulation here). […]

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