yes you are right about both points. Missing & and multiple of 4

Thank you. I was aware of the fact of 8bit vs 32bit. I haven't tried your code but it seems right. What did the trick for me in the end was the following: void putData64(byte* packet, int pos, uint64_t data) { uint32_t* out= (uint32_t*) (packet+pos+2); uint32_t* in= (uint32_t*) data; *(out++)= *(in++); *(out++)= *(in++); }

Just one more thing: are you sure ttyAMC0 is the correct port? On my ubuntu machine its ttyUSB0