Cross-talk square-wave?

Is there any load resistance at the end of the line? Dwight ________________________________ From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Noel Chiappa via cctalk <cctalk at classiccmp.org> Sent: Wednesday, March 29, 2017 6:40:22 AM To: cctalk at classiccmp.org Cc: jnc at mercury.lcs.mit.edu Subject: Cross-talk square-wave? Hi, a question about generic analog stuff. In the process of getting SD cards to work, Dave is seeing square-wave noise on a line. (1V of square wave, with pulses about 400ns long, running at 375kHz.) The line runs through a flat cable of modest length, along with other signal-carrying lines. (No, we were not smart, and didn't put ground lines between each pair of signal lines!) Could cross-talk cause this kind of noise? We would have thought that you'd only get spikes, associated with the rising and trailing edges of a signal in a parallel wire, not a whole square-wave. During the constant-current period in the middle of the pulse, there shouldn't be any cross-talk? Is there some mechanism I/we don't understand that could do that? (My guess is there's a leakage path in the circuitry on one end or the other, not cross-talk in the cable, but...) Thanks! Noel