user56910: I want 2 Arduinos communicating to each other, but only in one direction.  Arduino A = tx  and Arduino B = rx.
I have this working fine connecting CE and CSN on each NRF24 to pins 4 and 5 on each Arduino and using the nRF24L01 library.  No problem.
Since Arduino A will always ONLY be transmitting and Arduino B will always ONLY be receiving, can I do this with CE and CSN instead:
Arduino A --- put CSN to GND  and put CE to 3.3V
Arduino B --- put CSN to 3.3V and put CE to 3.3V
As to why?  This would simply help me interface the NFR24 to existing custom PCB's I've made which have no easy access to I/O pins.  My PCB's do have easy access to MISO, MOSI, and SCK.

user2881: It seems the CE pin is only used for TX, or to put it into standby. I think you can just connect it to VCC.
The CSN is required for SPI.
PS this RF24 library supports using the same pin for both CE and CSN. You'd have to define RF24_TINY for this to work.

user43025: No, you really do need the CE pin for both TX and RX modes.  See the following excerpts from the nRF24L01 datasheet.  They work practically the same for nRF24L01+:



56910: <p>I want 2 Arduinos communicating to each other, but only in one direction.  Arduino A = tx  and Arduino B = rx.</p>

<p>I have this working fine connecting CE and CSN on each NRF24 to pins 4 and 5 on each Arduino and using the nRF24L01 library.  No problem.</p>

<p>Since Arduino A will always ONLY be transmitting and Arduino B will always ONLY be receiving, can I do this with CE and CSN instead:</p>

<p>Arduino A --- put CSN to GND  and put CE to 3.3V
Arduino B --- put CSN to 3.3V and put CE to 3.3V</p>

<p>As to why?  This would simply help me interface the NFR24 to existing custom PCB's I've made which have no <strong><em>easy</em></strong> access to I/O pins.  My PCB's do have easy access to MISO, MOSI, and SCK.</p>
 2881: <p>It seems the CE pin is only used for TX, or to put it into standby. I think you can just connect it to VCC.</p>

<p>The CSN is required for SPI.</p>

<p>PS this <a href="https://github.com/nRF24/RF24/blob/master/RF24.cpp#L18" rel="nofollow noreferrer">RF24 library</a> supports using the same pin for both CE and CSN. You'd have to define <code>RF24_TINY</code> for this to work.</p>
 43025: <p>No, you really do need the CE pin for both TX and RX modes.  See the following excerpts from the nRF24L01 datasheet.  They work practically the same for nRF24L01+:</p>

<p><a href="https://i.stack.imgur.com/QGxFU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/QGxFU.png" alt="enter image description here"></a></p>

<p><a href="https://i.stack.imgur.com/qu7dI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qu7dI.png" alt="enter image description here"></a></p>
