I made a new 5101 SRAM board, and we tried it in Flash last week. When I made the board, I remembered some of the people on the pinball boards saying that the second chip enable was not needed. Ooops, should have take the time to download the schematic. Looking at the schematic, it immediately became obvious that I did need the active high chip enable. Very disappointing, and it did mean that we wouldn’t be able to get past this issue on 4/17/2012. I went back to the drawing board and came up with a way to create the extra chip enable using a FET. Of course, in that time, I was also looking around Mouser and found an Alliance memory chip that had both of the chip enables (AS6C6264A). It goes for about $1.54 in quantities 1. That meant making another board, and spending the time to drill it out, and solder the new connectors. Jumped back on the internet and ended up running into www.arcadechips.com. They had actual 5101 RAM chips for $4.50 which is about the same price as the parts that I needed to make my RAM replacement. When it would have been $20 for the chip, it made sense to update the design, but now, doesn’t seem to make much sense. Now the only thing that makes my design better is that it takes less current to hold the memory. Not a good enough reason, so I’ve just given up on this sub-project. The RAM chips should come in this week and we should be able to test them next Tuesday. Hopefully that will give us enough time to find any more problems before going down to Allentown for the pinball show at the beginning of May.
First rev of the boards for the open pinball project is getting pretty close. More on that when I finish them, and figure out how to put the schematics up on the web.