Zigbee Protocol
The two major frames we care about are transmit/receive frames and response frames.
Example Transmit Frame:
7E | 00 19 | 10 | 01 | 00 13 A2 00 41 B1 6D 1C | FF FE | 00 | 00 | 53 45 4E 54 20 46 52 4F 4D 20 42 | D1
Breakdown of the message:
Start Deliminator: signifies that the message is starting, always use 7E
1 byte
7E
Length of message: the number of bytes between length and checksum, not including length and checksum
2 bytes
00 19
Frame type: should be 10 for transmit, 90 for receive, and 8B for transmit response (but responses will be covered after transmit frames)
1 byte
10
Frame ID: lets you order messages, and associate transmit frames with their appropriate responses. (optional as far as I know, I was able to send out frames with the same IDs one after another
1 byte
01
64 Bit address: for transmit frames, it is the destination, for receive frames its the source
8 bytes
00 13 A2 00 41 B1 6D 1C
16 bit address: use FF FE for this. As far as we can figure that is the default value for when you dont have a 16 bit address, which we don’t.
2 bytes
FF FE
Broadcast radius: represents the number of hops in a mesh network the message should make before giving up if it cant reach the target. leave it at 00, which means no limit (best guess on this)
1 byte
00
Options: leave at 00.
1 byte
00
Message: this will contain the data that is actually being sent
variable bytes
53 45 4E 54 20 46 52 4F 4D 20 42
Checksum: the sum of the bytes between length and checksum, not including length and checksum
1 byte
D1
Example response Frame:
7E | 00 07 | 8B | 01 | FF FE | 00 | 00 | 00 | 76
Breakdown of the message:
Start Deliminator: signifies that the message is starting, always use 7E
1 byte
7E
Length of message: the number of bytes between length and checksum, not including length and checksum
2 bytes
00 19
Frame type: should be 10 for transmit, 90 for receive, and 8B for transmit response (but responses will be covered after transmit frames)
1 byte
10
Frame ID: lets you order messages, and associate transmit frames with their appropriate responses. (optional as far as I know, I was able to send out frames with the same IDs one after another
1 byte
01
16 bit address: use FF FE for this. As far as we can figure that is the default value for when you dont have a 16 bit address, which we don’t.
2 bytes
FF FE
TX retry count: the number of times the message was resent
1 byte
00
Delivery Status: 00 for success, anything else is failure
1 byte
00
Discovery status: 00 for success, 25 means root not found, which as far as I can figure, means that the destination wasnt found
1 byte
00
Checksum: the sum of the bytes between length and checksum, not including length and checksum
1 byte
76
How do the two frame types work together?
To receive a message, it’s simple. You receive a receive frame (which has the same basic structure as a transmit frame) that you can decode and use.
To send a message, you must first construct a transmit frame, send it to the Xbee. Then listen for transmit response to ensure that the packet was sent properly.
What has been done to get the Xbees working?
XCTU
XCTU is software that we can use to configure and run the xbees. We first used this software to send some test frames using the zigbee 3.0 protocol.
Logic Analyzer
We used a logic analyzer to read the signals being sent to and from the XCTUsoftware. This is how we know how the zigbee protocol works and what needs to be sent/recieved from the xbees. The xbees are actually quit simple. They use UART to communicate with XCTU/Arduinio/STM32. And they have an easy to follow protocol for constructing frames.
The difficulty with the xbees is the lack of documentation when it comes to the frames. This is where the logic analyzer was useful. We know how to construct frames for transmitting data and how to decode frames for transmit status and receiving data. XCTU also describes how to construct frames, using their frame builder software.
Ardunio
We got the xbees to work with an ardunio! One Xbee was plugged into a computer, listening for data, the other was wired to an ardunio. We then sent a transmit request to the Xbee from the ardunio! The xbee that was connected to the computer, recieved the message.
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