In datasheet , it said that the RPD can be read out at any time while nRF24L01+ is in receive mode. But if we want to read 0x09 register with SPI, we must let CE low. At this time , NRF is no longer RX mode at all ! How to do with this?
By the way ,is CD register just detect power in the RF you had already set regardless of P0 - P5 Address?
You don't need to set CE low to read configuration registers. Maybe you are thinking of the CSN line?
All configuration registers can be safely read during RX or TX mode, but if you want to write to the registers and change the RF configuration you will have to disable the radio, that is correct.
Oh my god! I always consider that reading register must low the CE! Thank you very much! I want to use 0x09 register to detect whether the RFchannel I used is disturbed by WLAN or not. Am I right?
You can use the RPD bit to try and evaluate if there is a lot of activity on the channel, that is correct, but keep in mind that it is not a fool proof method.
The activity on a WiFi network will change during use, and few networks are on 100% of the time, so you are not guaranteed to detect WiFi activity by using the RPD bit.
Another way to evaluate channel quality is to look at the retransmit count and packet loss between the TX and the RX whenever you try to transmit data. If you see a high number of retransmits and/or packet loss on a specific channel it could be a sign that you have a lot of interference on that channel.
