Are there going to be any problems mixing logic levels derived from chips driven by those different voltages? My initial view is "no" because of the 300mV clamping diode drops, but just checking other opinions...

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    \$\begingroup\$ Step 1: Check whether the 3.3V parts will run at 3V and vice versa. More often than not you can fun them from the same supply. \$\endgroup\$ – Matt Young May 7 '15 at 13:16
  • \$\begingroup\$ No problem running at either voltage \$\endgroup\$ – Dirk Bruere May 7 '15 at 13:23

I don't think that would be a problem - just make sure the 3V part's \$V_{OH}\$ is higher than the 3.3V part's \$V_{IH}\$ and the 3.3V part's \$V_{OL}\$ is lower than the 3V part's \$V_{IL}\$, and if you are really paranoid add a resistor on the line.

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  • \$\begingroup\$ What would added resistor accomplish? \$\endgroup\$ – Golaž May 7 '15 at 13:23
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    \$\begingroup\$ @Golaž The resistor will limit the current. This in turn limits the power dissipation within the ESD clap diode on the lower voltage device. Think about this: Your driving side is putting out 3.3V and can drive 30mA, and the receiving side runs on 3.0V. You'll get a 30mA current flow through the protection diode that way. If you otoh add a 1kOhm resistor just 0.3mA may flow and the input protection diode is all happy. \$\endgroup\$ – Nils Pipenbrinck May 7 '15 at 14:46

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