XBEE 3 rarely freezes 300-500 ms

XBee & XBee Gateway XBee - 802.15.4
1

Hi,

Problem Description
Sometimes in my XBEE communication I get random 300-500ms delays (See Image). When I scope the sender#S XBEE UART RX everything looks nice and with the same delay between messages (~10ms). When I scope the receiver’s XBEE UART TX most of the time (95-99%) it looks the same. But sometimes there is a huge delay of 300-500ms on the receiver XBEE UART TX. This happens 1-3 Times every 5 Minutes. During this delay no message gets lost. As soon as this big delay is over messages are send faster until it reaches normal interval again.

Screenshot 2025-10-31 at 17.29.47
Screenshot 2025-10-31 at 17.29.471552×257 13 KB

Architecture Overview
I have two XBEE 3 (XB3-24Z8ST), one as receiver and one as sender. Both XBEE are connected via UART to a MCU. Baudrate of UART is for both 460800. XBEEs are working in Transparent mode. The Serial Buffers of MCUs are set to 512. Both XBEE running newest Firmware and with 802.15.4 layer.
I send every 25ms 63 Bytes and additionally 39 Bytes every 100ms. The MCU at the sender just send these data via UART to XBEE, nothing more code/functionality. The MCU at the receiver XBEE just reads the data via UART from XBEE, nothing more code/functionality.

I also tried to increase the interval to 50ms for the 63 Bytes, but it shows exactly the same behaviour.

XBEE Configuration
Both XBEE are nearly same configured. I list some settings I think are important. If you need more, please let me know.

  • CH: 14
  • MM: 802.15.4 + Digi header w/ACKS [0]
  • CE: End Device [0]
  • RR: 3
  • PL: Highest [4]
  • CA: -32dBm
  • RN: 2
  • SM: No Sleep [0]
  • AP: Transparent Mode [0]
  • RO: 0 x character times
  • D6: RTS Disable [0]
  • D7: CTS Disable [0]

Does anyone had the same problem or/and knows what I’m doing wrong? I tried the last week to find the causing issue with no success.

Any help would be awesome. Thank you in advance!

2

What is the DL and DH set to on both radios?

What is the version of firmware on both radios?

3

Sender: DL = BEE6, DH = 0, Firmware = 2014

Receiver: DL = BEE7, DH = 0, Firmware = 2014

4

Are you setting the MY value on both radios as well to the above addresses? IE the sender would have an MY of BEE7 and the receiver an MY of BEE6 ?

5

Yes I do set the MY value as you have written

6

My guess would be that you are getting signals that are exceeding the CA threshold preventing the radio from being able to transmit. You may want to try using a different channel or run an Energy Detect (ED) to see what the noise level is getting to.

7

I did run ED. My Channel (14) was empty there but I just tried a few other empty channel and one did work. Thank you very much! Nice Support

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