29 Mar
2017
29 Mar
'17
12:53 p.m.
1v across 270K represents 3.7 microamps, which
isn't much, particularly
at 25MHz. (I assume that you're using SPI to access the card, but the
observation still holds).
Yup, I'm planning to use the SD card in SPI mode (at least for now).
And this line is the CS/CD line, so it's not even running at 25MHz. And
as Noel pointed out, this is happening without the SD card even being
plugged in. I'm not surprised at cross-talk, I'm surprised that the
cross-talk appears so clean. It's not spikes but fairly clean, 1V
square pulses.
And if you're using SPI, have you installed
pullups on unused pins?
Yup, I put in all the pull-ups.
I'd go to interleaved ground cable or UTP for the
device. Also, make
sure that your 3.3V supply is adequately decoupled--an SD card can draw
somewhere n the neighborhood of 100ma when operating, if the datasheets
are to be believed. I use a separate 3.3V LDO regulator at the SD card
socket.
Good point. I really should have put a good decoupling cap nearby and
the production card should have its own regulator.