Subject:
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memory not remembering...
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sun, 26 Jan 1997 03:51:59 GMT
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Original-From:
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{bendavis@MIT.}nospam{EDU}
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Viewed:
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2913 times
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I'm stumped.
In the process of assembling my first handyboard,
I have just reached the stage where I install the memory
(all previous checkpoints passed).
The computer successfully downloads the bootstrap,
sets the config register correctly, and dowloads pcode_hb.s19
file (at least, according to dl), but when I power-cycle the
board, the IC banner does not appear on the LCD screen- just the
row of 16 boxes.
Browsing through the handyboard archives, I found the following
suggestion by Fred for dealing with this specific problem:
> Success on the first bootstrap download and failure to write into RAM
> could easily be explained by a fault in the memory circuit. The
> memory circuit, which includes the 'hc373, the 'hc132, and the RAM
> chip itself, with about 27 signals going to the 'hc11, is by far the
> most complicated subsystem on the board, and any single problem
> anywhere in the circuit will cause the memory to not work, leading to
> the download error described.
>
> It's tedious, but the way to debug this is to individually examine the
> signals on the '373 and the ram chip using a scope or logic probe.
> With the HB turned on (not in bootstrap mode -- just turn it on and
> let it execute garbage), all of the appropriate signals (data bus,
> address bus, R/W line, '373 clock line) should be oscillating. If any
> are disconnected or shorted to power or ground it should be easy to
> see with the logic probe.
>
> Then with an ohmmeter and the board turned off, check that there is
> continuity where there is supposed to be (using the schematic as a
> reference) and no shorts between address and data lines.
Armed with an oscilloscope and an ohmmeter, I checked all the chips
and connections in the memory circuit, and found everything was
working as it should, except the R/W line for the ram chip (pin
27, according to my schematics). It does not oscillate but remains
at +5V.
What sort of oscillations should I expect on this pin? Do I need to
be trying to execute code or transmitting data to see the
oscillations?
I tried reheating and resoldering this connection but nothing changed.
(I reheated all the connections in the memory circuit just to be
sure)
I also noticed that this pin drops to ground when the board is turned
off, while the chip power supply (the adjacent pin 28) remains at
+5V, so the two of them aren't shorted together (which was my first
guess at what was happening)
Any thoughts or suggestions appreciated.
-max
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Message has 1 Reply:
 | | Re: memory not remembering...
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| Ben -- the pin 27 R/W line of the RAM should be connected directly to the R/W line of the 6811. I don't remember the pin # off hand -- it's 7 i think -- but just check the schematic. check the continuity first on the board. if that's ok, then check (...) (30 years ago, 26-Jan-97, to lugnet.robotics.handyboard)
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