nRF24L01+:the length of received data exceed 32

[I6believe]

hello,we use nRF24l01+ for the communication of IoT.There are a lot of terminals work at a same channel,when the controllers send CMD,we have found:the length of reading from R_RX_PL_WID exceed 32 bytes.we donot know the reason.

so,i want to ask if we have other protection mechanism except of judging the range of length(reading from R_RX_PL_WID).

would you give some advice,thank you very much.

[Håkon Alseth]

Hi,

If a payload is received with size > 32 bytes or size == 0, the FIFO must be flushed. If you read out this payload, the state machine inside the nRF24L01+ may go into a bad state.

This is mentioned in the PS, chapter 7.3.4:

Note: Always check if the packet width reported is 32 bytes or shorter when using the R_RX_PL_WID command. If its width is longer than 32 bytes then the packet contains errors and must be discarded. Discard the packet by using the Flush_RX command.

Cheers, Håkon

[Håkon Alseth]

If your RF address includes longer sequences of bit '0' or '1', like 0xFF or 0x00, or the address starts with patterns resembling the preamble (0x55/0xAA), then you are more prone to get an address match from demodulated noise. The CRC (if enabled) will filter out most of these, but if you use only 1 byte CRC, statistics state that 1 out of 256 "noise payloads" will pass as "OK".

Summarized:

• We recommend to have an RF address that does not start with 00/0xFF/0xAA/0x55
• We also recommend to use CRC, preferably 2 byte configuration.

Cheers, Håkon