How end devices communicate with each other in the XBee (Series 1) NonBeacon (w/Coordinator) network

Question

I setup a NonBeacon (w/Coordinator) network with three XBee Series 1 modules. One is configured as coordinator. The other two are configured as end devices. The firmware version and configuration are as below.

Firmare

Modem:  XBEE    Function Set    Version
XB24    XB24    802.15.4        10CD

Coordinator

Parameter            Value   Comments
CH (Channel)         0x0F    Identical
ID (PAN ID)          0x5241  Identical
DH                   0x0
DL                   0x0
MY (Source Address)  0xFF01  Unique
CE (Coord. Enable)   1  
A2 (Coord. Assoc.)   0x04    allow end devices to associate to it.

End device

Parameter            Value   Comments
CH (Channel)         0x0F    Identical
ID (PAN ID)          0x5241  Identical
DH                   0x0
DL                   0x0
MY (Source Address)  0xFF02  Unique
CE (Coord. Enable)   0  
A1 (End Dev Assoc.)  0x04    allow associate to coordinator.

When end device 1 sends out the data, the coordinator can receive the data, but the end device 2 can't. I want end device 2 to receive data from end device 1 in this network. My current solution is to let the coordinator broadcasts the data, so end device 2 can receive it. I'm not sure if this is good solution to resolve the communication issue among end devices. Is there any other solution?

Answer 1

With Digi XBee 802.15.4 modules (also know as Digi XBee Series 1 modules), there is no penalty to using broadcasts on the coordinate to speak with your end devices.

If on the other hand you wanted to be able to establish communication between any two Digi XBee 802.15.4 modules you'd need to use unicast addressing. Unicast addressing is performed the following way:

1. Set an address on each node by setting the MY parameter to a unique value
2. Set the coordinator's DL parameter to the MY value of the *end device node you wish to speak with.
3. Note that each end device will always be able to speak to the coordinator (the node with CE set to 1) by setting DL to 0.

It can be very clumsy to have to change the DL parameter on the coordinator to be able to speak with each end device in turn. This is why many end up using the Digi XBee radios in API mode.

If you download the manual from the Documentation section of Digi XBee 802.15.4 Support Page, you'll find a section entitled "API Operation". If you set the AP parameter to > 1 it will enable this mode.

If you send some data from an end device to the coordinator in API mode you'll see RX frames (API type 0x81) emerge from the radio. Likewise if you send packets of a similar format using API type 0x01) and specify the MY address of an end device as a destination, you'll see the data emerge from the serial port of the end device XBee.

If you search for "XBee API library" you'll find lots of useful links for libraries which can speak to Digi XBee modules using your language of choice such as this handy one for the Java language