is it possible to communicate two xbee S2 NOT using a microcontroller? (xbee to xbee or from xbee to PC)

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That would be dependent on what it is you wanted to do. If you want to send serial data, then there needs to be something on the other end to receive it. If you want to do ADC sampling, then using an interface board and connecting one radio to the PC and the other as an ADC input would be fine.