30 Mar
2017
30 Mar
'17
1:13 p.m.
From: Allison
FYI this is the same problem designers hit with DRAMS
back 40 years ago.
This didn't ring (pun not intended) a bell for me; can you say a bit more?
From: Chuck Guzis
I'll offer a suggestion that if your SD card
*must* be a significant
distance from its host
Like I said, this is a pre-prototype; on the production units, there will be
_no_ cable. The SD socket will be about 1-2" from the FPGA.
From: Dwight Kelvey
this behavior on my PDP-8/e where a 7474 flip flop
chip was bad. The
input looked great and the output was "half baked"
There's no chip at all on the driving end of the line (just that 470K
resistor); we see this with the SD card _unplugged_. And we see the exact
same thing on several lines.
I'm still not clear, from the discussion, how exactly that nice 'square-wave'
interference is happening - could it be capacitative crosstalk? (I'd have
thought capacitative cross-talk would be inverted - driving a positive voltage
on one 'side' of the 'capacitor' would, I would think, induce an
oppposing
voltage on the other. But I'm clearly no EE! :-)
Noel