LLCC68 datasheet(42/111 Pages) SEMTECH

42 / 111 page

LLCC68

Data Sheet

Rev. 1.1

DS.LLCC68.W.APP

Dec 2024

42 of 111

Semtech

LLCC68

www.semtech.com

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, but

limited to 254 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 61 .

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

6.2.3.3 Setting the Packet Length or Node Address

The packet length and Node or Broadcast address are not considered part of the payload and they are added automatically in hardware.

The packet length is added automatically in the packet when the packetType field is set to variable size in the command

SetPacketParam(...).

The node or broadcast address can be enabled by using the AddrComp field is in the command SetPacketParam(...). This field allow

the user to enable and select an additional packet filtering at the payload level.

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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