LLCC68 datasheet(41/111 Pages) SEMTECH

41 / 111 page

LLCC68

Data Sheet

Rev. 1.1

DS.LLCC68.W.APP

Dec 2024

41 of 111

Semtech

LLCC68

www.semtech.com

6.2.2 FSK Packet Engine

The LLCC68 is designed for packet-based transmission. The packet controller block is responsible for assembly of the received data

bit-stream into packets and their storage into the data buffer. It also performs the bit-stream decoding operations such as de-whitening &

CRC-checks on the received bit-stream.

On the transmit side, the packet handler can construct a packet and send it bit by bit to the modulator for transmission. It can whiten the

payload and append the CRC-checksum to the end of the packet. The packet controller only works in half-duplex mode i.e. either in transmit

or receive at a time.

The packet controller is configured using the command SetPacketParams(...) as in Section 13.4.6 "SetPacketParams" on page 87 . This

function can be called only after defining the protocol. The next chapters describe in detail the different frames available in the LLCC68.

6.2.2.1 Preamble Detection in Receiver Mode

The LLCC68 is able to gate the reception of a packet if an insufficient number of alternating preamble symbols (usually referred to 0x55 or

0xAA in hexadecimal form) has been detected. This can be selected by the user by using the parameter PreambleDetectorLength used in

the command SetPacketParams(...). The user can select a value ranging from “Preamble detector length off” - where the radio does

not perform any gating and tries to lock directly on the following Sync Word - to “Preamble detector length 32 bits” where the radio is

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

either drops the reception in RxSingle mode, or restarts 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.

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