SX1239IMLTRT Semtech, SX1239IMLTRT Datasheet - Page 48

• Manufacturer Part Number: SX1239IMLTRT
• Description: IC, RF RECEIVER, 1.02GHz, QFN-24
• Manufacturer: Semtech

Specifications of SX1239IMLTRT

• Applications: Wireless Sensor Networks, Automated Meter Reading, Home And Building Automation
• Receiving Current: 16mA
• Data Rate: 300Kbps
• Modulation Type: FSK, OOK
• Sensitivity Dbm: -120dBm
• Rohs Compliant: Yes
• Rf Ic Case Style: QFN
• No. Of Pins: 24
• Sensitivity (dbm): -120dBm
• Supply Voltage Range: 1.8V To 3.6V
• Operating Temperature Range: -40°C To +85°C
• Lead Free Status / Rohs Status: Supplier Unconfirmed

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
5.5.6. Packet Filtering
SX1239'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
Rev 3 - Jan 2011
ADVANCED COMMUNICATIONS & SENSING
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
Sync Word values containing 0x00 byte(s) are forbidden
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SX1239