Which nRF24L01+ SPI cmds require CE low?

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Which nRF24L01+ SPI cmds require CE low?

Postby pico » Thu Jun 21, 2012 5:51 am

I can't find anywhere in the data sheet a definitive list of SPI read or write operations that require CE to be low (or high, for that matter). I know the R_RX_PAYLOAD cmd is usually considered to need CE to be low for the fifo stack to pop properly (although I notice there has been discussion in these threads as to whether this is even strictly necessary on the latest versions of these devices). I've also seen someone mention in one of the threads here that setting the RF frequency via writing to RF_CH requires CE to be low, but haven't seen that documented or discussed anywhere else so far.

Is there a definitive list anywhere? Sorry if it's hidden somewhere in the data sheet (I'm working from the v2.0 product spec, 74 pages long.)

Thanks for the forum and the "quick start" tutorials. :-) Both great resources for anyone starting out with these devices.
Last edited by pico on Thu Jun 21, 2012 3:54 pm, edited 3 times in total.
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Re: Which nRD24L01+ SPI cmds require CE low?

Postby brennen » Thu Jun 21, 2012 12:07 pm

I really do wish that there was such a list of when to have CE at what value for all operations, but, alas, there isn't. I can tell you that for reading RX packets, you will *always* be able to pop the value from the RX FIFO automatically if you take CE low on nRF24L01 and nRF24L01+ devices. I actually haven't tested out whether the RX FIFO works as expected on either device while leaving CE high, though. I would definitely recommend that anytime you change any of the radio parameters (on RX or TX) that you have the CE pin low while you make the change over SPI, just to make sure the settings update properly.
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Re: Which nRF24L01+ SPI cmds require CE low?

Postby pico » Sat Jun 23, 2012 1:23 am

Interesting, and (from a relative newcomer's perspective) surprising. Perhaps it's expected that it's a bit more "obvious" when CE should/must be low once you get a bit more familiar with the devices?

Would it be worth taking the question to Nordic directly and see if they would input on the issue? If I got a response I could post back here and add to the general forum wisdom.

From some earlier posts, it seems that Nordic support are quite approachable -- from your experience, who would you suggest I send such a question to?
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Re: Which nRF24L01+ SPI cmds require CE low?

Postby brennen » Mon Jun 25, 2012 12:06 pm

Nordic support is quite excellent. The only bummer is that they're in Norway, so it typically takes a day or so before your questions get answered. If you do contact them, I think it would certainly be helpful to others if you could post their reply back here. :)
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