Digi XTend User Manual page 18

Modes of operation
The character timeout trigger can be disabled by setting RO to zero. In this case, transmission will not begin until RB
bytes have been received and are pending for RF transmission. The RB parameter may be set to any value between 1
and the RF packet size [refer to PK (Max RF Packet Size) parameter], inclusive. Note that transition to Transmit Mode
cannot take place during RF reception; the RF reception must complete before the radio can transition into Transmit
Mode.
If RB or RO conditions are met, the module initializes a communications channel. Serial data in the DI buffer is
grouped into RF packets (up to 2048 bytes in each packet, refer to PK Command), converted to RF data and is
transmitted over-the-air until the DI buffer is empty.
Channel initialization is the process of sending an RF initializer that synchronizes receiving modules with the
transmitting module. During channel initialization, incoming serial data accumulates in the DI buffer.
RF data, which includes the payload data, follows the RF initializer. The payload includes up to the maximum packet
size (PK Command) bytes. As the TX module nears the end of the transmission, it inspects the DI buffer to see if more
data exists to be transmitted. This could be the case if more than PK bytes were originally pending in the DI buffer or if
more bytes arrived from the UART after the transmission began. If more data is pending, the transmitting module
assembles a subsequent packet for transmission.
RF packet
The following diagram shows the RF packet components.
* When streaming multiple RF packets, the RF Initializer is only sent in front of the first packet.
RF initializer
An RF initializer is sent each time a new connection sequence begins. The RF initializer contains channel information
that notifies receiving modules of information such as the hopping pattern used by the transmitting module. The first
transmission always sends an RF initializer.
XTend RF Module User Guide 18