CRC (Cyclic Redundancy Check)
CRC is a checksum value appended to the end of the packet and mathematically derived from its content. The receiver performs the same calculation and discards the packet if it does not match. In this way a command corrupted during transmission is not reflected at the relay output; the result is not a wrong movement but the command being treated as never having arrived.
CRC is not encryption, it is an integrity check. It catches bit errors with high probability but provides no protection against deliberate alteration; that is the domain of encryption and authentication.
- Detection strength: as CRC length increases, the probability of an error slipping through falls quickly; a 16-bit checksum is a common choice for remote control packets.
- Behaviour: a packet that does not match is silently discarded, and a retransmission or the next periodic packet is awaited.
- From a safety point of view: this behaviour is the correct one; not executing an uncertain command is preferable to executing it.
If packets drop one after another in a heavily interfered environment, the system must interpret this as signal loss and bring the outputs to a safe position via the timeout. On the AXI side, the 250 ms timeout stated for the HCT402 is the counterpart of this logic: when no valid packet arrives, the motor goes to the safe centre position and oil flow stops.
Context in which this term is used: Wireless remote control installation: pairing, relay, safety