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Mark1960 · 28th Jun 2021, 4:32 pm

I think you have the address lines to the RAM from the wrong side of the buffers. This would prevent access to the RAM from the SCMP.

Is the diode supply switching to the RAM something you have already tested? I have experimented with putting the switching in the ground connection using a bc108 to avoid voltage drop as this also disables write enable when main supply is off. I wasn’t convinced this was really working well. I think I prefer to use a MAX818 or similar to also disable chip enable, though it might not be simple to connect the reset output to the SCMP via the edge connector.

If you have space use a small slide switch for the write protect instead of just a two pin header.

I don’t think you want pin 18 and 21 on the ram connected.

28th Jun 2021, 4:32 pm	#7
Mark1960 Octode Join Date: Mar 2020 Location: Kitchener, Ontario, Canada Posts: 1,297	Re: Ortonview PCB I think you have the address lines to the RAM from the wrong side of the buffers. This would prevent access to the RAM from the SCMP. Is the diode supply switching to the RAM something you have already tested? I have experimented with putting the switching in the ground connection using a bc108 to avoid voltage drop as this also disables write enable when main supply is off. I wasn’t convinced this was really working well. I think I prefer to use a MAX818 or similar to also disable chip enable, though it might not be simple to connect the reset output to the SCMP via the edge connector. If you have space use a small slide switch for the write protect instead of just a two pin header. I don’t think you want pin 18 and 21 on the ram connected.