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Modes of operation
9XTend-PKG-R RS-232/485 RF Modem User Guide
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RF initializer
An RF initializer is sent each time a new connection sequence begins. The RF initializer contains channel information
that notifies receiving modems of information such as the hopping pattern used by the transmitting modem. The first
transmission always sends an RF initializer.
An RF initializer can be of various lengths depending on the amount of time determined to be required to prepare a
receiving modem. For example, a wake-up initializer is a type of RF initializer used to wake remote modems from
Sleep Mode (Refer to the FH, LH, HT and SM Commands for more information). The length of the wake-up initializer
should be longer than the length of time remote modems are in cyclic sleep.
Header
The header contains network addressing information that filters incoming RF data. The receiving modem checks for
matching a Hopping Channel, VID and Destination Address. Data that does not pass through all three network filter
layers is discarded.
Refer to the ‘Addressing’ section of the “RF Communication Modes” chapter for more information.
CRC (Cyclic Redundancy Check)
To verify data integrity and provide built-in error checking, a 16-bit CRC (Cyclic Redundancy Check) is computed for
the transmitted data and attached to the end of each RF packet. On the receiving end, the receiving modem computes
the CRC on all incoming RF data. Received data that has an invalid CRC is discarded [refer to the ‘Receive Mode’
section].
Receive mode
If a modem detects RF data while operating in Idle Mode, the modem transitions to Receive Mode to start receiving RF
packets. Once a packet is received, the modem checks the CRC (cyclic redundancy check) to ensure that the data was
transmitted without error. If the CRC data bits on the incoming packet are invalid, the packet is discarded. If the CRC is
valid, the packet proceeds to the DO Buffer.
The following figure shows the Receive Mode Data Flow.
* Refer to the ‘Address Recognition’ section for more information regarding address recognition.