Found these inside a non-working 71B

[MikeSD]

(03-12-2018 11:50 PM)Dave Frederickson Wrote:  I'm a bit confused by the daisy-chain diagram above. The "main 5 chips" are all daisy-chained, out to in, but according to the schematic, U5, the ROM, has it's DOUT unconnected and VDD is connected to DIN on both U5 and U6, the Port(0.1) RAM. Can you clairfy?

Dave

I was justbguessing. Conceptually that was what I thought was going on. Likely there should be only 4 devices not 5. Pin 9 on that end chip went to the Math on the other 71B I think. I just ran it to my ram as the next device.

I'm still not sure what to expect if I insert a 64k there. MEM doesn't show 80k but I don't know that it should. I doubt it's defective because the other stuff works fine on the original 71B they came from.

What operations can I do to see if that RAM is actually there other than MEM which returns 15931 consistently? Any chance there is some other configured necessary? I do know it's not configured as port ram. Any chance it's there but not visible because of some limitation?