LJelect Sub GHz FSK/OOK Transceiver Module : Data Sheet : Page 54

LJ1269HC

Rev1.0 Page 54 Web: www.ljelect.com

In Fixed length mode the Message part of the payload that can be encrypted/decrypted can be 64 bytes long. If the address

filtering is enabled, the length of the payload should be at max 65 bytes in this case.

In Variable length mode the Max message size that can be encrypted/decrypted is also 64 bytes when address filtering is

disabled, else it is 48 bytes. Thus, including length byte, the length of the payload is max 65 or 50 bytes (the latter when address

filtering is enabled).

If the address filtering is expected then AddressFiltering must be enabled on the transmitter side as well to prevent address byte

to be encrypted.

Crc check being performed on encrypted data, CrcOk interrupt will occur "decryption time" before PayloadReady interrupt.

5.5.6. Handling Large Packets

When Payload length exceeds FIFO size (66 bytes) whether in fixed, variable or unlimited length packet format, in addition to

PacketSent in Tx and PayloadReady or CrcOk in Rx, the FIFO interrupts/flags can be used as described below:

 For Tx:

FIFO can be prefilled in Sleep/Standby but must be refilled "on-the-fly" during Tx with the rest of the payload.

（1） Prefill FIFO (in Sleep/Standby first or directly in Tx mode) until FifoThreshold or FifoFull is set

（2） In Tx, wait for FifoThreshold or FifoNotEmpty to be cleared (i.e. FIFO is nearly empty)

（3） W rite bytes into the FIFO until FifoThreshold or FifoFull is set.

（4） Continue to step 2 until the entire message has been written to the FIFO (PacketSent will fire when the last bit of the

packet has been sent).

 For Rx:

FIFO must be unfilled "on-the-fly" during Rx to prevent FIFO overrun.

（1） Start reading bytes from the FIFO when FifoNotEmpty or FifoThreshold becomes set.

（2） Suspend reading from the FIFO if FifoNotEmpty clears before all bytes of the message have been read

（3） Continue to step 1 until PayloadReady or CrcOk fires

（4） Read all remaining bytes from the FIFO either in Rx or Sleep/Standby mode

Note AES encryption is not feasible on large packets, since all Payload bytes need to be in the FIFO at the same time to

perform encryption

5.5.7. Packet Filtering

LJ1269HC 's packet handler offers several mechanisms for packet filtering, ensuring that only useful packets are made

available to the uC, reducing significantly system power consumption and software complexity.

Sync Word Based

Sync word filtering/recognition is used for identifying the start of the payload and also for network identification. As previously

described, the Sync word recognition block is configured (size, error tolerance, value) in RegSyncValue registers. This

information is used, both for appending Sync word in Tx, and filtering packets in Rx.