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MS05000 Budget Logic Analyzer Probe Set Design
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Gandalf_Sr:
Thanks, you guys pulled me back from the ledge there! I was ready to jump.
TK:
Is it possible to set the threshold from the scope or you are limited to 3.3V and 5V logic only?  Does it work with ECL (-1.3V)?
Gandalf_Sr:
The threshold settings on the scope make no difference, the voltage level translation IC sets the threshold level depending on the voltage at VccA which is set either by the Vadj pot or the Vext voltage depending on which way the switch is thrown.

My understanding of ECL is that all the voltages are negative so it won't work; unless maybe you can connect it up backwards and set Vadj at around 2V then you'd have to reverse the logic as a low would be +1.75 volts and high would be +0.9V? It might work.
TK:
What happens when you set the threshold in the scope that is different to 3.3V and 5V?  for example if you use the 3.3V board and then set the threshold to a different setting, does it still capture the signals correctly?  Or they need to match (board and scope setting)?
Gandalf_Sr:

--- Quote from: TK on May 20, 2020, 05:14:37 pm ---What happens when you set the threshold in the scope that is different to 3.3V and 5V?  for example if you use the 3.3V board and then set the threshold to a different setting, does it still capture the signals correctly?  Or they need to match (board and scope setting)?

--- End quote ---
The threshold settings in the scope don't do anything and can be ignored (they do provide a variable voltage to the front connector but my circuit does nothing with it).

The datasheets for the SN74AXC8T245 voltage level translator (VLT) has the table below to give the threshold voltages and, as you can see, it's purely a function of VccA (VccB is running at 3.3V all the time).  The DS90LV047A driver ICs take the 3.3V logic levels from the B side of the VLT and send them as differential LVDS signals to the scope.  If you built with SN74LVS8T245 VLT ICs (the 5V version) then you'll have to look up the equivalent table in the datasheet.
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