Xbee 3 latency unstability in strict 802-15.4

XBee & XBee Gateway XBee - 802.15.4
1

Hi,

We use the zigbee to synchronize diffrent units.
We use a transmitter adressing a broadcast message to remote units that output a sync signal we need a fixed latency but variation of about 1ms are acceptable.

All Modules XBRR-24 with 802.15.4 FW.
They are all configured the same between TX and RX modules. Only TX receives data on its DI input.

  • Same PAN
  • Same channel,
  • MY 0
  • DH 0
  • DL FFFF
  • CE End Device
  • BD 115200
  • RO 3 Bytes
  • Transparent operating Mode
  • NO API
  • Not sending AT commands
  • The payload is 28bytes.
  • The rest is default values (no ack, no encyption, … )

The delay between DI pin of TX and DO pin of RX is

  • with S1 Pro modules [6.960 ; 7.720] ms → 0.760ms It’s stable variation
  • With S2C non pro modules [6.960 ; 7.780] ms → 0.760ms It’s stable variation for the 1st minute
  • After the 1st minute, it shifts to [7.560 ; 8.780] ms → 1.22ms witch is still acceptable but to the limit.
  • With the XBRR-24 is goes crazy [7.2; 9.5] ms → 2.3ms in average but regularily it makes jumps up to 12ms.

Note that changing the TX module to S1 or S2C doens not impact the terrible results with the XBRR-24 modulas as TX. The issue seems to be mainly at the RX side.

What can explain the unstability? how to resolve it?

Thanks,

Johan

2

Johan, This is something that really should be addressed by submitting a support case at my.digi.com

However, I can tell you that you are comparing different hardware which use different processors and versions of the IEEE 802.15.4 stack. There will be differences in how they preform.

3

May I suggest if this is a simple point to point connection that you change the addressing so that you are using the same MY and DL values. For example, your remote radio may use an MY of 2 and a DL of 1. The base would then use an MY of 1 and a DL of 2. By using this same addressing scheme, you can use the same base with different remotes.