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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.
