Must transmit very slowly

I have 2 XBP24-B - one setup as Coordinator, the other as Router/End Device in AT mode. They are communicating at 19,200, 8 bits, 1 stop, no parity. One is connected to a PC, via USB, and the other to a microcontroller.

My basic problem is that if I transmit bytes any faster than 1 Hz, they start getting lost.

I did a test with a very simple setup. When I press a key on my keyboard, it flashes an LED on the microprocessor.

If I hit the key about once per second, it works just fine. However, if I speed up much beyond that, they start getting lost.

This is a one-way communication and I have verified that the Xbee is the problem. If I watch the DOUT LED, it also stops flashing if the rate it too fast.

Surely I should be able to reliably transmit faster than 1 byte/sec?


I did a little more testing and realized this problem is only in one direction. I switched the rolls of the devices to verify it wasn’t a hardware issue.

With the Xbee attached to my microcontroller and set as the Coordination and the one attached to my PC as End Device, I can send data at it much faster.

So the problem seems to be that I have to send data TO an END DEVICE very slowly, but not the other way around.

I’m pretty sure I have all the sleep options turned off.


In case somebody else runs across this, I figured out the problem from another thread. Apparently the XBee’s have this poor performance problem when they are in broadcast mode instead of unicast mode. More info can be found here: 802.15.4 Addressing#knowledgebase

Justinb - Correction. It is not a poor performance issue with the radio so much as a limitation on the standard that is commonly not understood. However the KB article you refer to is correct.