In SX Microcontrollers, SX/B Compiler and SX-Key Tool, g_daubach wrote:

Hello Robert,

well, I overlooked the on-board voltage regulator, so this is what actually makes the difference between a 3.3V and 5V Version.

I think the SX is tolerant to 5 V on inputs when running at 3.3V. The Propeller is designed for 3.3 V so it comes with clamping diodes at its inputs, rated slightly above 3.3 V. When you apply a higher voltage, a relatively high current will flow through these diodes to Vdd. This is why series resistors in the Propeller input lines are necessary to limit this current. The SX, on the other hand, is designed for 5 V (and less) supply. Therefore, the clamping diodes are rated above 5 V. So 5 V at an input should be OK when the SX is running at 3.3 V.

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