How do you set the channel on a XBee PRO series 2?
I've got three XBees. 2x PROs and a standard, all series 2s. I've configured one PRO and one standard to be router/endpoints on channel 0 and PAN 234 (this is the default channel and PAN ID when selecting the "XBP24-B"/"XB24-B" "ZNET2.5 ROUTER/END DEVICE AT" profile (version 1247 for both).
However the one PRO I've set with the "ZNET 2.5 COORDINATOR AT" profile has a channel of E (though if I keep flashing the device with the same profile, this changes from 12-F).
Obviously if the coordinator doesn't have the same channel, nothing will work, but I can't see any way of setting the channel manually..?
The CH setting in X-CTU is read only, and I can see any other UI element to change the channel:
I've even been into the terminal and typed (words in brackets are what the terminal returns):
+++ (OK) ATCH (E) ATCH0 (ERROR) ATCH 0 (ERROR) ATCH00 (ERROR) ATCH 00 (ERROR) ATCH E (ERROR) ATCHE (ERROR)
I've Googled and Googled to no avail. incredibly frustrating, can anyone help?! I've had them working previous as a matter of fluke as I kept flashing the hardware until the channel numbers match up, but this is obviously ridiculous!
Answer
Channel selection with the XBee ZB (S2, S2B, S2C) series of modules works differently than with the XBee 802.15.4 (S1) modules. Channel selection is automatic with ZB (as opposed to it being manual with the 802.15.4 modules).
You normally never need to manipulate the channel selection parameters with ZB. Modules find each other and associate with each other if they can.
If your modules just can't seem to find each other it usually comes down to a mismatch in the PAN settings (ID), security settings (LK), or network joining permission settings on the coordinator (NJ).
Not a lot of information exists on the web outside of the Digi's XBee ZB OEM manual. For reference sake, channel selection with ZB works like this:
- XBee ZB Coordinator is powered up
- The XBee ZB Coordinator reads its SC parameter and builds a list of candidate channels to scan
- The XBee ZB Coordinator then performs an energy scan on each candidate channel
- The XBee ZB Coordinator then chooses the channel with the least amount of energy on it
This procedure aims to pick a channel with the least amount of noise on it be it from microwave ovens, WiFi networks, or anything else that might be transmitting on the 2.4GHz frequency band.
Any router or end devices joining a network with consult their SC parameters first, then they will try and search for networks they can join which match their PAN and security parameters. They will join and stay joined to the first network they can--with some minor exceptions (see the JV and NW parameters, for example).
If you want to force a channel selection you must set the SC parameter to enable only a single channel. The SC parameter is a bitmask1. Each bit set in the mask will enable one additional channel. What's tricky about this parameter is that the first bit (bit 0) is not channel 0, it's channel 11 (0x0B). For ease of use, if you wanted to lock an XBee ZB to a single channel here would be the values:
+---------------+---------------+------------------+-------------------------+
| Channel (Dec) | Channel (Hex) | XBee ZB SC Value | XBee Availability |
+---------------+---------------+------------------+-------------------------+
| 11 | 0xB | 0x1 | All |
| 12 | 0xC | 0x2 | All |
| 13 | 0xD | 0x4 | All |
| 14 | 0xE | 0x8 | All |
| 15 | 0xF | 0x10 | All |
| 16 | 0x10 | 0x20 | All |
| 17 | 0x11 | 0x40 | All |
| 18 | 0x12 | 0x80 | All |
| 19 | 0x13 | 0x100 | All |
| 20 | 0x14 | 0x200 | All |
| 21 | 0x15 | 0x400 | All |
| 22 | 0x16 | 0x800 | All |
| 23 | 0x17 | 0x1000 | All |
| 24 | 0x18 | 0x2000 | All |
| 25 | 0x19 | 0x4000 | S1, S2B, S2C (not S2) |
| 26 | 0x1A | 0x8000 | S1 only |
+---------------+---------------+------------------+-------------------------+