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XW-111™ Wi-Fi Digital Sensor Users Manual
Section 6: Xytronix Compact Data (XCD) Format
The XW-111 sends data contained in a TCP/IP packet. To keep the packets small, and conserve battery
power, they are not XML/HTTP.
XW-111 Digital 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
nd
MSb is set, the packet is a salt request. Both the encrypted and salt request bits 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.
Input Status
Single byte to indicate the present status of the inputs. The LSb is input 1 with the next bit being input 2.
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-111 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.
Xytronix Research & Design, Inc.
Interval
4 bytes
4 bytes
Function Description Code
XW-111 Packet
Xytronix Compact Data (XCD) Format
Battery
1 byte
0x0002
Input status
CRC
(4C11DB7)
1 byte status
4 bytes
Page 39
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