Xbee end devices changes channel?

Hi!

I am doing one project with Xbee modules, and I have been testing Xbee network for several months. Recently, I had one strange “bug”, and I can’t figure out what is the problem.

I have XbeePro series2 (XBP24-B) set as ZNET 2.5 Coordinator API, and three Xbee S2 (XB24-B) set as ZNET 2.5 END DEVICE/ROUTER API.

Each module is controlled by a PIC microcontroller. After powering up, PIC sends “JV=1” AT command (enabling Channel Verification) to end devices, so end device will join specific channel only if there is a coordinator on that channel.

Few times I noticed that after some time, coordinator didn’t communicate with end devices properly. After some searching what went wrong, I noticed that two end devices changed channel, from channel 12 to channel 17. I don’t know how is this possible… Microcontroller is sending some log messages, and one of these messages is end device’s current channel, so I noticed that sometimes end device leaves its current channel, and returns that operating channel is 0.

Could you tell me few reasons, when could end device/router leave it’s operating channel?

I read section about leaving a network in digi’s document no. 90000976_G, but I don’t use none of the mentioned AT commands ( ID, SC, ZS, NR0, NR1).

Also, how it is possible that end device joins channel 17 if coordinator is working on channel 12?

Thank you!

BR