In another thread I talked about putting the EEPROM in a socket and swapping MPUs and the EEPROM to retain all settings when changing game themes. I realize that setting up the game again is no big deal for some people, but I for one find it a PITA.
Of course to swap MPUs for game changes, one must have some spares. In any case, I decided to take it a step farther and put the EEPROM on the MPU. I did a search, but only found info on someone doing it on another type of game. So I decided to do it on my S+ and go ahead and document it in case someone else wanted to know if it could be done.
The answer is to that is yes, and it works fine.
Briefly a little background. The EEPROM is a I2C (serial) based chip. That means it only needs four wires to operate. +5v, ground, SCL and SDA. The way it is implemented on the S+, they put a few of the support components (pull-up and pull-down resistors) on the motherboard.
What I did was I used a 16 pin socket to build the 'carrier board' instead of fabricating a separate board. I used the top half for the chip, and the bottom half for the 4 extra components (3 resisters and 1 capacitor). Then I just wired everything up under the socket and ran the 4 lines out as seen in the first picture.
Luckily, the SCL and SDA outputs are easy to get to on the MPU (besides at the connector). They are located at the output of the two resistors shown in the second picture.
So, the idea is to mount the 'carrier' in the area shown in the third picture and tie the 4 wires in right there. SCL & SDA right to the resistors, and tap off +5v and ground of the chip right below them.
For some reason they have a parallel RC network tied between 5V and ground on the motherboard going to the EEPROM. So to eliminate any problem with those lines, I just pulled the resistors up from the board where they run down to the connector and soldered the wires directly on the ends. This also means one can leave a EEPROM on the motherboard, since it will be in effect disconnected. For someone with just two themes, this means they could modify just one MPU and still be able to swap back and forth. The modified one will use the EEPROM on the MPU and the unmodified one will use the EEPROM on the motherboard.
The total time to actually build this was about 45 minutes. It took longer to figure out the wiring on the motherboard, because the schematic has an error which has both ends of the capacitor going to ground, so I had to trace it out by hand. The total cost in parts is about $5, but I already had everything in my parts bin.
So now if I want to swap game themes, I just need to swap the MPU and go. Of course reel strips (or reels with strips already on them) and glass too, but no setup time and any credits etc., are intact. I donβt have that many game themes and never will, so this mod is not for everyone. Mainly I just did it (like my other projects) to prove it will work.
Note: That missing socketed chip in the last picture is that DUART I asked about, that is not needed for home use.
The carrier.
The MPU and the two resistors that are the SCL (top) & SDA (bottom) lines
The finished project
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