RF65 datasheet(48/72 Pages) ETC2

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Page 48

RF65

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ADVANCED COMMUNICATIONS & SENSING

DATASHEET

The receiver sees the AES decryption time as a sequential delay before the PayloadReady interrupt is available.

In Fixed length mode the Message part of the payload that can be 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 decrypted is also 64 bytes whether address comparison is

enabled or not. Thus, including length byte, the length of the payload is either 65 or 66 bytes (the latter when address

comparison is enabled) at max.

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

5.5.5. Handling Large Packets

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

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

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

perform decryption

5.5.6. Packet Filtering

RF65'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.

5.5.6.1. 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 to filter packets in Rx.

Every received packet which does not start with this locally configured Sync word is automatically discarded and no

interrupt is generated.

When the Sync word is detected, payload reception automatically starts and SyncAddressMatch is asserted.

Note

Sync Word values containing 0x00 byte(s) are forbidden

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