**ID = 65535 => order to all slaves (no ack)
**ID = 65000 to 65499 => order to a group of slave (no ack)
**ID = 1000 to 64999 => order to an a unique slave (ack)
*2 bytes for the function (FCT_HIGH and FCT_LOW)
*1 byte for the number of data bytes to transmit (N_BYTE)