SX1232
WIRELESS & SENSING
DATASHEET
otherwise it's stopped. The CRC check is performed if CrcOn = 1 and the result is available in CrcOk indicating that the
CRC was successful. An interrupt (PayloadReady) is also generated on DIO0 as soon as the payload is available in the
FIFO. The payload available in the FIFO can also be read in Sleep/Standby mode.
If the CRC fails the PayloadReady interrupt is not generated and the FIFO is cleared. This function can be overridden by
setting CrcAutoClearOff = 1, forcing the availability of PayloadReady interrupt and the payload in the FIFO even if the CRC
fails.
5.5.5. Handling Large Packets
When PayloadLength exceeds FIFO size (64 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 FifoEmpty to be set (i.e. FIFO is nearly empty)
3) Write 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 FifoEmpty is cleared or FifoThreshold becomes set.
2) Suspend reading from the FIFO if FifoEmpty fires 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
5.5.6. Packet Filtering
The SX1232 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, value) in RegSyncConfig and RegSyncValue(i)
registers. This information is used, both for appending Sync word in Tx, and filtering 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
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).
Rev 3 - August 2012
Page 60
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