LLCC68 datasheet(40/106 Pages) SEMTECH

40 / 106 page

LLCC68

Data Sheet

Rev. 1.0

DS.LLCC68.W.APP

July 2019

40 of 106

Semtech

www.semtech.com

to “Preamble detector length 32 bits” where the radio will be expecting to receive 32 bits of preamble before the following

Sync Word. In this case, if the 32 bits of preamble are not detected, the radio will either drop the reception in RxSingle mode,

or restart its tracking loop in RxContinuous mode.

To achieve best performance of the device, it is recommended to set PreambleDetectorLength to “Preamble detector length

8 bits” or “Preamble detector length 16 bits” depending of the complete size of preamble which is sent by the transmitter.

Note: In all cases, PreambleDetectorLength must be smaller than the size of the following Sync Word to achieve proper

detection of the packets. If the preamble length is greater than the following Sync Word length (typically when no Sync

Word is used) the user should fill some of the Sync Word bytes with 0x55.

6.2.3 FSK Packet Format

The FSK packet format provides a conventional packet format for application in proprietary NRZ coded, low energy

communication links. The packet format has built in facilities for CRC checking of the payload, dynamic payload size and

packet acknowledgement. Optionally whitening based upon pseudo random number generation can be enabled. Two

principle packet formats are available in the FSK protocol: fixed length and variable length packets.

6.2.3.1 Fixed-Length Packet

If the packet length is fixed and known on both sides of the link then knowledge of the packet length does not need to be

transmitted over the air. Instead the packet length can be written to the parameter packetLength which determines the

packet length in bytes (0 to 255 bytes, but limited to 254 Bytes when the address filtering is activated, see Table 13-56).

Figure 6-3: Fixed-Length Packet Format

The preamble length is set from 8 to 65535 bits using the parameter PreambleLen. It is usually recommended to use a

minimum of 16 bits for the preamble to guarantee a valid reception of the packet on the receiver side. The CRC

operation, packet length and preamble length are defined using the command SetPacketParams(...) as defined in

Section 11. "List of Commands" on page 57.

6.2.3.2 Variable-Length Packet

Where the packet is of uncertain or variable size, then information about the packet length (0 to 255 bytes, but limited to

254 Bytes when the address filtering is activated, see Table 13-56) must be transmitted within the packet. The format of the

variable-length packet is shown below.

Figure 6-4: Variable-Length Packet Format

CRC Checksum

Whitening

Preamble

8 to 65535

bits

Sync Word

0 to 8 bytes

Payload

1 to 255 bytes

CRC

0, 1 or 2 bytes

Address

0 to 1 byte

CRC Checksum

Whitening

Address

0 to 1

byte

Payload

0 to 255 bytes

CRC

0, 1 or 2 bytes

Preamble

8 to 65535

bits

Sync Word

0 to 8 bytes

Length

1 byte

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