I am sending a pulse to the expansion pin of an FPGA board which I am monitoring using an oscilloscope. Why is the oscilloscope reading the pulse in the attached photo? Why it is not a pure square pulse?

enter image description here

  • 2
    \$\begingroup\$ It looks like it's set for AC coupling? If so try DC and see what it looks like. \$\endgroup\$ – PeterJ May 29 '15 at 4:44
  • \$\begingroup\$ Right, in AC coupling this is wha5 it looks like. Also maybe your probe's ground is not connected to the right place. \$\endgroup\$ – Gregory Kornblum May 29 '15 at 4:58
  • \$\begingroup\$ It could also be a probe that has not had its frequency compensation set properly. \$\endgroup\$ – Michael Karas May 29 '15 at 9:43

This looks like a measurement issue. Either you have a broken scope probe (broken signal connection), a disconnected ground wire, or the scope is set to AC coupling.


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