I am using the Devantech SRF05 ultrasonic sensor and the Axon MCU. I want to to check if port F1 is receiving anything, so the code I am using is bit_is_clear(PINF,1), however the Axon does not seem to be running the function. I can't find this function in any of the header files I have. I saw on the forum that it was in sfr_defs.h, but I downloaded the source code for the Axon and the AVRlibc and I cannot seem to find it. Does anyone have any suggestions of where I can find it?