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

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

ovrebekk — Thu, 30 Sep 2021 09:01:35 GMT

Your register configuration looks OK, but there is no point writing to the FEATURE register when EN_AA = 0.

The FEATURE register is only active when EN_AA is enabled. Without EN_AA enabled you never send/receive ACK packets.

Best regards
Torbjørn

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

sukru — Wed, 29 Sep 2021 07:49:54 GMT

I also opened new case about it I dont know how to share it but the issue name is "Minimum time possible to send 32byte data with NRF24L01 module ?".

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

sukru — Wed, 29 Sep 2021 07:41:29 GMT

1-Yes, I am using 2Mbps mode

2-This is my init function that you can see above and "EN_AA" register is set to 0h.

3-After I send 32byte data to NRF24L01, I set the CE pin high for 10us,

4- I use NRF24L01 which is connected to the MCU on Receiver side.

As a summary : I am waiting for TX_DS to be high and when TX_DS is high I send 32byte data and wait for TX_DS again. One period of this process are 424us (TX_DS High --->TX_DS High again ).

Do I have to wait for the time on air to send new data?

Best regards.

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

ovrebekk — Tue, 28 Sep 2021 15:23:42 GMT

In general it is not recommended to reply to an old case with a new question, even if it is somewhat related. You should open a new ticket instead.

I assume you are using 2Mbps mode if you are trying to get 32 bytes across in this short time?

When do you set the CE signal on the TX side?
It should be possible to set it the same time you start writing data over the SPI interface, in order to avoid having to wait for the TX rampup after the payload is sent to the chip.

What is the state of your EN_AA register?
If you disable ACK completely then you should be able to send packets quicker. The main drawback is that you lose the ability to use dynamic payload length (and acks/retransmissions won't work obviously).

When you say "on the receiver side", do you mean you want to get the interrupt on the receiver, or the data needs to be read out and ready in the host MCU?

Best regards
Torbjørn

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

sukru — Tue, 28 Sep 2021 11:19:50 GMT

I've been trying to send fast data with NRF24L01 for a long time. In order for the project to meet its requests, 32bytes of data must be on the Receiver side at a maximum of 400us. I'm currently seeing 424us. The content of the code is as follows:
I init in NRF24L01 "main"
After 10ms, the first data is gone and after that, I send data by looking at the TX_DS bit. Whenever the TX_DS bit is one, I send 32bytes of data again and the transactions are carried out in this way at regular intervals.

I didnt use ARC to avoid delays.

My SPI works on 10MHZ and I also see this in SCK pin of NRF24L01.

There is not any switching between RX and TX, When I initialize one of the NRF24L01 as a TX it stays always in TX mode.

My SPI send 1 byte to the NRF24L01 at 2.9us and wait for other 1byte at 650ns (until 32byte)

What should I do to gain 24us? Should I focus on SPI or NRF24L01 initializatin?

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

ketiljo — Tue, 06 Mar 2018 12:25:12 GMT

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.

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

Andrew Kohlsmith — Mon, 05 Mar 2018 15:22:51 GMT

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?

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

ketiljo — Mon, 05 Mar 2018 15:18:25 GMT

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.

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

Andrew Kohlsmith — Mon, 05 Mar 2018 14:12:35 GMT

Thank you ketiljo. From your description it sounds like my minimum timeslot period should be the PLL startup time plus the actual transmission time, plus a few microseconds for inter-packet separation. i.e. something around the 200us mark.

If I need to get that time smaller, I could use the nRF51822, which has dramatically improved PLL setup times, although now I can't find where I read that.

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

ketiljo — Mon, 05 Mar 2018 12:57:02 GMT

The 130 µs is the startup time of the radio, in TX or RX mode.

When it's in RX mode, it will receive continuously. There must be small gap between the packets to avoid collision, a few µs is enough, . The RX will process the packet on the fly to as long as there's a free FIFO.