Bally/Stern MPU Memory Expansion Board

20 April, 2011 (13:27) | Pinball | By: admin

It should come as no surprise to readers of my blog that I’ve created yet ANOTHER daughter board for the Bally/Stern pinball MPU. This time the board greatly increases the available RAM and ROM. You might be asking “why would I want that”. Well… most people probably won’t need or want that at this stage of the game. In the future, however, I would like to see a community of developers grow up around this board and use it to create new and amazing game code for older games. At a minimum I would like to see simple things like attract mode added to games that did not originally have any kind of attract mode (think early “chimer” games).

In addition to adding substantial RAM and ROM these boards are also fully compatible with original game code making them a relatively cheap and easy way to upgrade and repair original MPUs potentially replacing as many as 7 ICs which would originally have needed their sockets replaced with a single CPU socket based daughter board. The RAM is all contained in a single NVRAM so there is no more need for batteries. A jumper is provided to select between “Bally” and “Stern” RAM modes allowing compatibility with games that originally used a single 5101 RAM (all Bally and Stern MPU-100).

Unlike my other EPROM replacement daughter boards this board connects to the CPU socket. This was a requirement to achieve maximum RAM and ROM but also makes it easier to use -17 and MPU-100 boards with newer game code. Converting a -17 for use in an MPU-200 game is as simple as installing my board and replacing a couple of capacitors in the clock circuit to increase the clock speed to MPU-200 specifications. I cover that conversion in an article here.

Here are some pictures of my current working prototypes. I expect to have these available within a couple of months. I’ll have some more detail about the exact memory map and usage of the board at that time. In the mean time I can say that there will be approx. 8X the original ROM and 20X the original RAM!

This is an early prototype as indicated by the wires hacked all over the place.