08 April 2009

XBee Series 2 - JV Channel Verification

Damn it. Why do the simplest things always take hours to complete? I'm using XBee Series 2 cause I really didn't know what I was buying. Series 1 or Series 2? To a newb, sounds like 2 is the shiny. Why buy an out-dated series 1? Nobody wants last year's model.

If I would've done my homework, the series 1 (also called 802.15.4) are the most reliable, easiest to use. So of course, I'm using Series 2.

I first attempted to use them as described in the ZNet 2.5 Modules Product Manual, one as a coordinator, one as an end device. No luck. I followed every instruction I could find on the web. Nada.

Just by dumb luck, I found that if I flashed two radios as ZNET 2.5 ROUTER / END DEVICE AT and then set the Destination Address of each to point to the other, it appeared to work. I could send data to and from the serial ports. I used them in this way for the tweet-a-w/e foundation and had good success.

For an end device called WHITE that will talk to another end device named PINK, use X-CTU and load the ZNET 2.5 Router / End Device AT firmware. Go to the X-CTU Terminal tab and type:
+++
ATRE
ATNIWHITE
ATDNPINK
ATWR
Here's the X-CTU file for WHITE.

But now I'm trying to send analog data from one to the other and I'm back to nada. The data receive light blinks and it appears to read data, but nada bit comes out of the UART.

I decided to go back to square one and reconfigure as coordinator and end device. Sounds easy? Right. Took me two nights to get the devices associated. What's associated? From page 14 of the 802.15.4 manual (and not in the series 2 manual):
Association is the establishment of membership between End Devices and a Coordinator. The establishment of membership is useful in scenarios that require a central unit (Coordinator) to relay messages to or gather data from several remote units (End Devices), assign channels or assign PAN ID.
The series 2 manual seems pretty decent. I've read many sections and need to sit down and attempt to read more. Too bad though that it doesn't mention parameter JV Channel Verification. Which is the parameter that finally made a difference.
[update] maybe I was looking at the wrong manual. The one I ref'd above is the Series 2 Manual. The JV parameter is mentioned in the ZNET 2.5 manual.

When setting up a coordinator and associated end devices, there's a few things that you need to do:
  • After writing the firmware, go to the terminal and do a ATRE to reset to factory values. I would've saved lots of time if I realized that previous values were not being overwritten between firmware loads.
  • Make sure that the PAN ID is set the same on both devices. I suggest that while debugging, you have both devices connected to your computer via an adafruit XBee Adapter or SparkFun XBee Explorer and use X-CTU to monitor. You need to verify that the Operating PAN IDs are the same when they're trying to associate.
  • Set each device to a unique Node ID
  • The coordinator destination address should be set to DH=0, DL=FFFF
  • The end device destination address should be set to DH=0, DL=0
And for basic communications, that should be it. No need to set destination address of the end device explicitly to the coordinator. The 0's do that for you.

My problem though was my coordinator was on channel F and my end device was channel D. I could see this while watching them start up, but I could not figure out WTF.

Finally by going thru every parameter on both devices using X-CTU, I realized that JV Channel Verification was the ticket. This is described in the X-CTU tool as:
Set/read the channel verification setting. If enabled, a router will verify a coordinator exists on the same channel after joining or power cycling to ensure it is operating on a valid channel, and will leave if a coordinator cannot be found (if NJ=0xFF). If disabled, the router will remain on the same channel through power cycles.
In English, this means that if your devices are on different channels and JV is disabled, you're fricked cause the router won't go to another channel to associate.

Change JV to enabled and reboot the device:

+++
ATJV1
ATWR
ATFR

I've uploaded the configuration to my coordinator named BLUE that has ZNET 2.5 COORDINATOR API firmware. And an end device named PINK that has ZNET 2.5 ROUTER / END DEVICE AT firmware.

What do you think? Leave a comment.

4 comments:

Radu said...

Hi, i folowed yours instructions and worked like charm. You are a nights saver :D. Keep up the good work!

Serge said...

just spent hours to solve same issue...

did not find answer via goggle...
I was missing key word "JV".


for sure as soon as I got the solution by myself (too time consuming), it become easy to find this excellent article ! Unfortunately too late for me.

anyway good article,... I like the story at the beginning with series 2... I did the same path too !

Artem said...

Thank you very much. Googled your post by something like "Xbee doesn't change channel". Spent an awesome night before it, once my working network of XBee's suddenly stopped to work!

Billy1010 said...

But what happens if i want to assign the channel for the coordinator..

isn't that possible?