Random packet : nRF2401 / uMiRF and SPI question

Wireless & IoT
1

Hi everyone,

As mentioned by someone in previous posts, uMiRF can pick up random packets from the air with a short address (say 8-bit). I’m also having this problem even with 16-bit CRC…

This seems very “amazing” coz I think the probability of finding a packet with a correct 16bit CRC - preamble and a correct address is very low?? Does anyone have an explanation on this?

And for SPI between MCU (i’m using Atmel mega48) and nRF2401, do you guys sample your data at the falling edge or at the rising edge of clock?? From the timing diagrams on the datasheet, it seems that both will do…please correct me if I’m wrong.

Thanks !!!

Will

2 
SPCR = (1<<SPE)|(1<<MSTR)|(1<<SPR0); // /8 clock (8Mhz/8 = 1Mhz)

Is the SPI setting I used (so CPOL and CPHA are both 0). The rest of the code is in the avr code forum.

I also get some random packets and had to add some additional validation of the received data to check for this.

/Lars

3

I find this to be a problem when using 8bit crc. when using 16bit crc I never got a bad packet. I’m also using 8 bit address.

I guess with cellphones, wireless home phones, wireless Lan’s, radios and all other stuff some packets might be accepted.

4

I’m using the MSP430 (with a SPI USART) and we found that we needed to use the CKPH option for the SPI. In effect, phase shift the data off the clock. While the configuration worked with CKPH = 0, whenever we read data from the device it was wrong. (This is using the two 10k resistors that tie the MISO and MOSI lines together)

5

so it looks like a MCU problem not the transceiver