28112Re: [midatlanticretro] Re: vintage SRAMs self healing
- Nov 14, 2012
I didn't see your link before and just took a look at your homebrew tester. It really needs some more work to tighten up the circuit before proceeding with further experiments. So that you will have a good baseline to work with. I don't think it's a complete kludge :) but you really like to have a solid working platform. Yours can can be done with some minimal steps - it's the same wiring but now you have to solder them :) You can dedicate a type of daughter card which would hold the Ram test socket -- or dedicate the whole Superproto card as a tester. The daughter card would plug into the top(or rear) of your SuperProto card. You can wire a generic I/O interface on the SuperProto card from the 6522. Use some right-angle headers/connectors to mate the two on top of the SuperProto card. Have one daughter card dedicated for the 2102 and another for the 1101.
The important issue is to keep the wiring short, point to point, use plenty of ground pins on the headers/connectors - the typical layout is to alternate the signals with grounds along the headers pins to reduce Crosstalk - and having plenty of ground pins helps to avoid Ground Bounce when many signals are switching simultaneously on the bus. Since there's a minimal amount of passive components on there, you can improve the quality even further prior to adding the Ram tester circuit on there. Create a ground plane on there using the grid of plated through-holes - say a grid with a gap of 300mils and connect each side of the grid straight to the ground bus. The more pcb area thats covered with a ground plane improves the signal integrity.
BTW, the capacitance on a ribbon cable is not any significant amount higher than a FR4 PCB - approx 2pf/inch vs 1pf/inch. Ribbon cables have been used everywhere for the past 40years on boards fatter than my butt. It's all in how you organize the signals. This is where you reduce the crosstalk/signal intergrity issues.
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