cs8900a always returning 0x5555

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Dear all

I'm trying to use a CS8900a ethernet controller in one of my designs.
I connected it to the CPU according to the app notes (16 bit IO mode,
CPU's /CS conneced to AEN and /SBHE, I try to use IO mode). I tripple
checked everything against the checklist in the app note an83-3 and so
far everything looks ok. Hooking up a logic analyzer showes that
timeings are ok also. When I plug in a 10BaseT cable from the RJ-45 on
my board, the LINK-LED on both sides light. But when i try to read the
signature from the register IOBASE+OAh, i always get 0x5555. In fact,
i only get the value 0x5555 for all addresses between 0x300 and 0x30e.

I'm now struggling with this problem for days and would really
apreciate any help on this. I searched the net and found an old thread
about the same issue, but there was no solution to the problem posted.
I'm currently realy out of ideas, so any hints on what to check etc.
are welcome.



Re: cs8900a always returning 0x5555
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Well, we didn't think it was timing because you assured us that it wasn't.  :-)

Good work finding the bug!!

Re: cs8900a always returning 0x5555

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You are of course right here. What I was lookign fore (since I
consider myself being a beginner) were some general tips/hints what
else to check. After this post I did the folowing things

- solder out the oszilator. The lan link went away which for me was
some indication that the osizlator seemed to do it's work.
- Used a scope to check the oscilaotor oszilating. It did, but I heard
that due to the capacitance of the probe it could oszilate during
measure and not before and after. Anyways, I then concluded that the
oscilator most likely woule work.
- replaced the cs8900a with aother one. Since this gave the same
results, and since the wireing was ok not much more other than the
timeing (IMHO) was left over.

I probably would have expected from the experts some advice like well,
what you describe leaves open 1) a malfuncitoning chip, 2) oszilator
not working or 3) you are worng with your asumptions or 4) any other
advice. Being a newbee, one soon feels sort of trapped from such a
situation if no one answers. In general I'm keen to learn and even if
an advice would not have hit the nail it surely would have helped
learning. Not geting a single reply in such a crisis (sorry but to me
it was sort of) just makes you feel dumb / even more lost if other
questions around your own post are answered within minutes.

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Yeah, you have no idea how lucky I am now. The hardware design for
this project is now complete and I'm now happy to complete the

Many thanks for your reply. It's highly apreciated! :-)


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