24L01+ end of transmission minimum time between transmitters (TDM)?

[Andrew Kohlsmith]

I have a theoretical question involving 6 24L01+ devices in PTX mode and one 24L01+ device in PRX mode.

Assuming a synchronized system, when one PTX finishes transmitting how long must the "dead time" be before another PTX may transmit on the same channel so the PRX can reliably receive messages? The datasheet mentions that the 24L01+ requires 130us from the time the transmitter stops to the time the PLL can lock to the incoming signal, but in my scenario the 6 PTXs are all transmitting data to the PRX which is always listening; there is no radio turnaround time in the meaningful sense.

(I understand that after transmitting, the 24L01+ automatically flips to RX but in my application nothing is ever transmitting back to the PTX; not even an ACK.)

To add some concrete numbers to this, assume 2MBit data rate, 5 byte address, 32 byte payloads and 2 byte CRC. This would give 329 bits per packet or 165us to transmit a message.

e.g. at t=0, PTX #1 transmits its message. at t=165us, PTX #2 transmits. At t=330us, PTX #3 transmits, etc., etc.

Is this feasible? Assuming tight enough timing sync, will this work or do I need to put some dead time between PTX #1 and PTX #2? If so, how much dead time?

Thanks

[ketiljo]

When the RX is up and running, after the 130 µs, there's no additional delay. The RX will receive packets with a few µs delay between packets. Unless you have to turn around and transmit, the nRF24L01+ will do fine.

But remember that you need to clock out the data as well.

[Andrew Kohlsmith]

I understand that the RX does not need to go through RXUP again, but in my scenario PTX1 will go through TXUP (130us) and then transmit (~195us). Then PTX2 will need to transmit, going through its TXUP and then transmit.

With careful and precise enough timing I suppose I can have PTX2 going through TXUP while PTX1 is still transmitting (e.g. have the next transmitter TXUP while the current transmitter is transmitting its packet) to minimize the dead time.

While in TXUP state, a transmitter is not actually doing anything on-air, is it? It's just waiting for the PLL to lock?

[ketiljo]

The carrier is turned on a few µs before the modulation is started. The 130 µs is mainly used to start the oscillator and lock the PLL.