RF65 datasheet(49/72 Pages) ETC2

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Page 49

RF65

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ADVANCED COMMUNICATIONS & SENSING

DATASHEET

5.5.6.2. Address Based

Address filtering can be enabled via the AddressFiltering bits. It adds another level of filtering, above Sync word (i.e. Sync

must match first), typically useful in a multi-node networks where a network ID is shared between all nodes (Sync word)

and each node has its own ID (address).

Two address based filtering options are available:



AddressFiltering = 01: Received address field is compared with internal register NodeAddress. If they match then the

packet is accepted and processed, otherwise it is discarded.



AddressFiltering = 10: Received address field is compared with internal registers NodeAddress and BroadcastAddress.

If either is a match, the received packet is accepted and processed, otherwise it is discarded. This additional check with

a constant is useful for implementing broadcast in a multi-node networks

As address filtering requires a Sync Word match, both features share the same interrupt flag SyncAddressMatch.

Please note that the received address byte, as part of the payload, is not stripped off the packet and is made available in

the FIFO.

5.5.6.3. Length Based

In variable length Packet mode, PayloadLength must be programmed with the maximum payload length permitted. If

received length byte is smaller than this maximum then the packet is accepted and processed, otherwise it is discarded.

Please note that the received length byte, as part of the payload, is not stripped off the packet and is made available in the

FIFO.

To disable this function the user should set the value of the PayloadLength to 255.

5.5.6.4. CRC Based

The CRC check is enabled by setting bit CrcOn in RegPacketConfig1. It is used for checking the integrity of the message.

The checksum is calculated on the received payload and compared with the two checksum bytes received. The result of

the comparison is stored in bit CrcOk.

By default, if the CRC check fails then the FIFO is automatically cleared and no interrupt is generated. This filtering function

can be disabled via CrcAutoClearOff bit and in this case, even if CRC fails, the FIFO is not cleared and only PayloadReady

interrupt goes high. Please note that in both cases, the two CRC checksum bytes are stripped off by the packet handler

and only the payload is made available in the FIFO.

The CRC is based on the CCITT polynomial as shown below. This implementation also detects errors due to leading and

trailing zeros.

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