NRF24L01 （the Carrier Detect functionality CD） 载波检测功能的问题？

jackyard

我在24L01的手册上看到了有the Carrier Detect functionality 这个功能，
In RX mode a carrier detect signal is avaliable. The carrier detect is a signal that is set high when a RF signal
is detected inside the receiving frequency channel. The signal must be FSK modulated for a secure
detection. Other signals can also be detected. The Carrier Detect (CD) is set high when an RF signal is
detected in RX mode, otherwise CD is low. The internal CD signal is filtered before presented to CD register.
The RF signal must be present for at least 128μs before the CD is set high. How to use the CD is described
当接收端检测到射频范围内的信号时会把CD的最后一位变高，同时会保持128US。如是在Enhanced ShockBurst™ 模式下，使用方法如下：

In Enhanced ShockBurst™ it is recommended to use the Carrier Detect functionality only when the PTX
device does not succeed to get packets through, as indicated by the MAX_RT IRQ for single packets and by
the packet loss counter (PLOS_CNT) if several packets are lost. If the PLOS_CNT in the PTX device indicates
a high rate of packet losses, the device can be configured to a PRX device for a short time (Tstbt2a +
CD-filter delay = 130μs+128μs = 258μs) to check CD. If CD was high (jam situation), the frequency channel
should be changed. If CD was low (out of range or jammed by broadband signals like WLAN), it may continue
on the same frequency channel, but you must perform other adjustments (a dummy write to the
RF_CH clears the PLOS_CNT).
就是只有在发送端没有发送成功的情况下，再去变成接收模式，去检测CD。我现有的一个问题，我想在发送前去读一下CD。在读CD时是接收态的。这样是为了防止空中的碰撞。我在测试，有一个模块我记它一直发数据。别一个一直while去读CD。有一个问题是，是刚开始可以读到CD是高，只会读到2次。再就没有了，我不知道是不是在读完CD后，还要请一些寄存器。有做过24L01的朋友，请指点一二，就是载波检测功能的使用？？？

allen3161

能把你怎么做的发出来看一下吗？

zplmcu

进入到发送数据时候会清除CD寄存器， PDF对CD检测讲的不是很清楚

你可以测试下 两个发送地址 频道什么都一样，PTX端CE一直拉高（发送完之后直接进入到STANDBY2模式）
试试看

allen3161

回复【2楼】zplmcu
进入到发送数据时候会清除cd寄存器， pdf对cd检测讲的不是很清楚  
你可以测试下 两个发送地址 频道什么都一样，ptx端ce一直拉高（发送完之后直接进入到standby2模式）
试试看
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我是你这么做的，但是还是不可以？

allen3161

这个接收的检测放和发送方的速度有没有关系呢？

linye

没有用过NRF24L01用过NRF24L01+，在NRF24L01+的数据手册里是这么写的：

6.4 Received Power Detector measurements
Received Power Detector (RPD), located in register 09, bit 0, triggers at received power levels above -64
dBm that are present in the RF channel you receive on. If the received power is less than -64 dBm,
RDP = 0.
The RPD can be read out at any time while nRF24L01+ is in receive mode. This offers a snapshot of the
current received power level in the channel. The RPD status is latched when a valid packet is received
which then indicates signal strength from your own transmitter. If no packets are received the RPD is
latched at the end of a receive period as a result of host MCU setting CE low or RX time out controlled by
Enhanced ShockBurst™.
The status of RPD is correct when RX mode is enabled and after a wait time of Tstby2a +Tdelay_AGC=
130us + 40us. The RX gain varies over temperature which means that the RPD threshold also varies over
temperature. The RPD threshold value is reduced by - 5dB at T = -40°C and increased by + 5dB at 85°C.


09 RPD
Reserved 7:1 000000 R
RPD 0 0 R Received Power Detector. This register is called
CD (Carrier Detect) in the nRF24L01. The name is
different in nRF24L01+ due to the different input
power level threshold for this bit.

注意到：
The status of RPD is correct when RX mode is enabled and after a wait time of Tstby2a +Tdelay_AGC=
130us + 40us.
会不会TX模式下RPD(对nrf24l01来说就是CD)是不能用的啊。

jackyard

谢谢各位，网友的热议。CD还是读出来的是0.发送和接收的地址，频道一模一样，就是一个是发，一个是接收，发的会10MS发一次，接收端。用一个while来一直的读CD。可一直是0.有没有nordic的工程师，出来说说啊。

Alvin007

楼主是否有结果？

Alvin007

也正在研究 一起讨论

5楼提到：
“会不会TX模式下RPD(对nrf24l01来说就是CD)是不能用的啊”

我认为，应该是在接收模式下进行载波检测，如果有冲突则等待；如果没有冲突，则转为发送模式进行发送。

也就是说，都是在接收状态下去检测链路是否被占用。

不知道是不是这样理解

klmt

我最近也在整这个，防碰撞，，PDF上说的很明白就是在接收模式下才能进行载波检测，，但是怎么来清除这个CD 呢，只有在发射模式下才清除标志吗，楼上咱俩可以讨论一下子，呵呵我QQ231299903

ghbb88

mark

cgswh

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