I have a application where I need to broadcast data from 1 device to several others at about 9600bps, and I plan to use XBee-PRO® ZB devices.
There is only 1 coordinator, no routers, and all the other End devices.
If they share the same PAN ID, the broadcast solution looks fine because all will receive the data. And I still get two way data if the end devices need to tell something to the coordinator.
My question is that if this kind of broadcast application is a abuse of Zigbee, and if there is a better product for this application.
Yes, broadcast is very unrealiable under ZB. Each broadcast requires about 5 seconds to ‘clear’ as it needs to be repeated up to 3 times by all nodes, so includes back-off and random delays. You cannot get any reliable data movement during that time.
Look at the S1 raw 802.15.4 if you want to broadcast in a point-multi-point manner.
In your situation, life is a bit weirder for ZigBee. The coordinator will NEVER send anything to end-devices. When they wake, the poll their parent for work. Assuming the coordinator is the parent, then your broadcast is not only sent (just in case any other routers need), but a copy is queued into the buffer for each child. The children (even if awake) don’t see the broadcast. If the child wakes within the time defined by SP of the coordinator/parent, then the child/end-devices is told data is waiting and in the next poll, it fetches it. If the child/end-devices wakes too late, the buffer has been cleared and it never knows any broadcast was sent.
I see that raw 802.15.4 is probably much better!
Also the problem with end devices not receiving could be corrected by using routers instead, since I don’t have any special power requirements, but 802.15.4 is enough.
Also ZB would have a limit on 10 direct connected devices, while my application doesn’t even require the concept of paired device…
My only question: why does the series 1 and series 2 Pro xbee have different ranges for the same 63mW of tx power?
But I suppose to some extent it is politics - range is a very subjective because it is measured in a LAB by fancy meters. I trust the S1 numbers more - the S2 are perhaps inflated because so many ZigBee competitors put the 3000 meter range that Digi needs to justify matching it [:(]