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Operation
After the device transmits on a channel, it will not transmit on that channel again until the minimum
TX off time has been met, which is greater than 100 ms. It is useful to have many channels in your
channel mask, so transmissions are less likely to be delayed.
European requirements also state that only 100 seconds of transmission may occur over the period of
an hour on 200 kHz of spectrum. This method simplifies and optimizes the calculations of spectrum
use over the period of one hour. The standard states that the more channels you have, the more
transmission time you have in a one hour period. Calculate the effective duty cycle based on the
number of available channels enabled as follows:
Effective Duty Cycle = (number of channels * 100)/3600.
For example, if you enabled two channels you would have an effective duty cycle of 5.6%.
The XBee SX 868 RF Module uses a sliding bucket algorithm to calculate usage over the period of 1
hour for each channel. Each bucket accumulates for 6 minutes.
This device has a maximum of 28 AFA channels to choose from, and channels can be excluded by
setting the channel mask (CM) to reduce them. Since not all countries allow for all of these channels,
the set may be dramatically smaller for some countries. For a complete list, refer to www.digi.com.
Single frequency mode band mode
When you set the channel mask to 0x20000000, the device is in a single frequency mode, and the
frequency is 869.85 MHz. In this mode:
LBT+AFA mode is disabled.
n
The device assumes no duty cycle requirement (or 100% duty cycle).
n
The PL is automatically limited to 5 mW to comply with the single frequency mode
n
requirements.
Serial communications
RF Modules interface to a host device through a serial port. Using its serial port, the device
communicates with any of the following:
Logic and voltage compatible UART
n
Level translator to any serial device (for example, through an RS-232 or USB interface board)
n
UART data flow
Devices that have a UART interface connect directly to the pins of the XBee SX 868 RF Module as
shown in the following figure. The figure shows system data flow in a UART-interfaced environment.
Low-asserted signals have a horizontal line over the signal name.
XBee® SX 868 RF Module User Guide
Single frequency mode band mode
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