The CD register has a single bit that represents carrier detect.
This table is copied from the nRF24L01 product specification (page 55).
|Reserved||7:1||0000000||R||Only ‘0000000’ allowed|
One example of how this might be used would be in response to packet loss, to detect jamming (see Appendix E of the nRF24L01 Product Specification). The device must be set to receive mode for at least 258 µs (130 µs for the radio to enter Rx mode and 128 µs for it to detect a carrier wave). If a jamming signal is detected, then one might initiate a channel-hopping routine. This driver presented in this report does not use this functionality, since the channel it uses is fairly low in traffic and we certainly hope not to be jammed maliciously!