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This is good stuff. Just goes to show with a bit of detective work what can be done. Once you have all the bit locations that need changing you'll now doubt try it on the actual ROM code which is where, as you know, you'll hit the checksum error. I did manage to circumvent this on a MPU4 test ROM. It was really poke and hope and I really only (eventually) disabled the error routine as I couldn't find where or how the checksum was stored?

Sounds good Ed but it's lost me on the code side. But great work 👏

A lot of this is trial and error, but it shows that it's possible to find settings to change attributes of the game, just takes a while to hunt them down. The speed changes on the hold sequence and the roulette wheel. Same principle as the credit change to 10, Load Accumulator A (LDA) with a value of #$96 and it will decrement (DECA) every scan until the value becomes 0 (Branch if Not Equal to 0 will loop on its self to address 7908), then it will move to the next line. So if we make the value smaller to 45, the pause will be less time, then bigger to FF it will take longer. So to change the value for FF search for the HEX string of 37 36 86 96 then change to 37 36 86 FF Save and reload in the emulator.

First step forward... Just had a quick look at the assembly code and had a look for the 50p coin credit recognition. I looked for where the A & B accumulators were being loaded for the number 5. There were 6 instances so I changed them all to another number which changed the credits recognised. I then back tracked back one by one to find the right address. The code is: The instruction is at address: 6281 LDB #$05 which translates to C6 05 in HEX. Load Accumulator B with the HEX value of 05. If the HEX string in changed form 05 to and hex number up to FF that number of credits are recognised. 0A in Hex is 10. I searched in the HEX editor for the string 26 F7 C6 05 I changed it to 26 F7 C6 0A then saved and reloaded the rom in to the emulator This now recognises 10 credits for a 50p.

No worries Ed. If you need any pics of my ace nifty nudge then no probs .