ControlByWeb XW-110 User Manual page 44

Xytronix Compact Data (XCD) Format (XW-110)
Section 7: Xytronix Compact Data (XCD) Format (XW-110)
The XW-110 sensors send data contained in a TCP/IP packet. To keep the packets small, and conserve
battery power, they are not XML/HTTP.
XW-110 Temperature Sensor Packet
Function Code MAC Address Salt
2 bytes 6 bytes
Function Code
Indicates how the packet should be interpreted. If the MSb of the first byte is set, the packet is
encrypted. If the 2
should not be set at the same time.
MAC Address
The MAC address used by the wireless interface, MSB first. This also matches the serial number of the
device.
Salt
Random number requested from the master to be included in the information packet sent back to the
master. This salt is included to prevent replay attacks to the master. Only used when using encryption.
Interval
Indicates the period of the transmissions in seconds.
Battery percentage
Indicated the estimated battery life remaining. The MSb, if set, indicates the device is being externally
powered.
Temperature
Temperature as recorded by the connected sensor as an IEEE-754 floating point value, MSB first. For
the XW-110-Plus the temperature values start with sensor 1 and end with sensor 3.
CRC
The CRC is computed over the entire packet minus the 4 bytes reserved for the CRC result. The CRC is
computed using the 0x4C11DB7 polynomial and is included to make sure the packet has not been
tempered with. CRC is only present when encryption is used.
Procedure
The XW-110 will send the packet as described above once the interval has expired. The CRC is not
included in unencrypted packets and the salt field is not used.
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4 bytes
nd MSb is set, the packet is a salt request. Both the encrypted and salt request bits
Function Description Code
XW-110 Packet
XW-110™ WiFi Temperature Sensor Users Manual
Interval Battery
4 bytes 1 byte
0x0001
Temperature CRC
(4C11DB7)
4 byte IEEE- 4 bytes
754 float
Xytronix Research & Design, Inc.