Monitor connections

Is there a way to monitor signals in existing wires? For example, with an oscilloscope and probe I can watch voltage changes. Is there a standard way to connect to an existing, working device, and monitor and record its switching over time? Such would seem to be desirable for peeking at proprietary "wake up" chirps, and to monitor device communications to establish its protocol interface.

On old phone systems, a coil device could be used to "copy" the phone signal without tapping the voltage. I guess I'm looking for something similar for general purpose wire use.

Best regards, Rick C. Hodgin

Reply to
Rick C. Hodgin
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Xilinx has ChipScope and Altera has SignalTap. These are logic analysers that you can put inside the FPGA and attach to signals to monitor the state of your design.

There are some caveats: Typically changing the probe state requires a recompile of your design (which can take hours) The amount of state you can record is limited by the internal memory in your device

but it's still far better than trying to route signals outside and using a real logic analyser.

If you want better visibility and quicker turnaround you'll have to run things in simulation rather than on the FPGA.

Theo

Reply to
Theo Markettos

I've done the logic analyzer thing before. A board I have in production has 9 signals it can drive on a 10 pin connector to see internal state. To be most useful I used a mux to select which internal signals drive these outputs. There is an undocumented control register in the FPGA to control the mux. But even with this if I need a signal that I hadn't planned for, I have to reprogram the FPGA.

To Rick C.'s question, I have never seen a probe intended to save you the trouble of accessing one end of the wire. A needle can be used to pierce the insulation if needed.

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Rick
Reply to
rickman

A current probe can do that, with significant limitations, of course!

Reply to
Tom Gardner

or a needle stuck in the middle of the wire (assuming we're talking discrete wires and not a trace inside an IC). There are also insulation displacement quick-connects made for tapping into automotive wiring. On the other hand I've heard the OP has moved on, so we'll probably never really know what the intent of the question really was.

Reply to
GaborSzakacs

Not sure what you are really looking for, there are some methods around trying to decrypt the bitstream:

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Reply to
Arne Pagel

A current probe measures current, not voltage. It is a pretty poor way to measure signals.

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Rick
Reply to
rickman

You can also capacitively couple signals into a probe, but you only get the higher frequencies due to the filtering effect. That might be OK for GHz signals, but not for DC.

Theo

Reply to
Theo Markettos

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