Found these inside a non-working 71B

[Paul Berger (Canada)]

(03-13-2018 02:00 AM)MikeSD Wrote:  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.

Yes on a base 71B the memory chain 0 will only have 4 devices, the four built in 4K RAM modules. The fifth module, center bottom is the OS ROM and is hard configured so it does not show up in any chain.

(03-13-2018 02:00 AM)MikeSD Wrote:  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.

When it is wired up correctly I would expect that you would see 64K more of memory when you run the MEM command. I would be extremely surprised if it got configured as port RAM since that requires the first few nibble of the module to be a specific pattern, and SRAM being a volatile memory device it will lose its content when not power up, and then when power is reapplied the contents would be random. The 71B provides Vcc to the memory as long as there are good batteries installed or it is plugged in.

I have done this before I know that it works, the only difference is in my setup, Dout (pin 9) from U7 was disconnected and routed to Din (Pin 8) on the first 32K RAM and then Dout from 32K_1 was routed to Din on 32K_2 and since I was breaking into the middle of the chain Dout from 32K_2 is connected where Dout from U7 used to be so now the chain is U6 -> U7 -> 32K_1 -> 32K_2 -> U8 -> U9 -> 32K added on top of U9 -> HPIL.

If you add your modules at the end of the chain, in your test 71B which has just the base RAM, you would connect Dout from U9 (the via under the resistor is effectively the same point) to Din of the first 32K there is no need to connect Dout of the second 32K to anything and if the modules are good they should configure as system RAM.

(03-13-2018 02:00 AM)MikeSD Wrote:  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?

There is the showport command but it is broken in the 1BBBB version of OS but there is a LEX version of showport that works properly. Dave Frederickson put together a package of tools for use with the FRAM module that includes a modified version of a program that I wrote to dump the memory configuration called membuf. Of course to load any of these you will need access to mass storage which is going to mean you will need HPIL. I guess I should add that if you want to use HPIL on you test system with the 32K modules wired in you will need to properly break into the chain and route Dout from the second 32K to Din of the next module and that will require some wiring changes on the board.