S2-LP datasheet(55/90 Pages) STMICROELECTRONICS

55 / 90 page

S2-LP

Packet handler engine

DocID029944 Rev 1

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Table 52: PHR frame

Bit string index

1-2

5-15

Bit mapping

R1-R0

FCS

L10-L0

Field name

Mode switch

Reserved

FSC type

Data whitening

Frame length

In particular:



MS is always set to 0b (mode switch not supported).



R1-R0 are always set to 00b



FCS is set to:



0b if CRC mode 3 is selected.



1b if CRC mode 5 is selected.



DW is set to:



0b if whitening is disabled, register WHIT_EN = 0.



1b if whitening is enabled, register WHIT_EN = 1.



L10-L0 are set equal to the 11 bits LSB of the packet length registers set by using the

two registers PCKTLENx (x= 1, 2) as: PCKTLEN1 × 256 + PCKTLEN0. The packet

length is from 0 to 65535 bytes (MHR + MAC Payload + CRC), then LEN_WID = 1b (2

bytes length field transmitted).



Payload: the main data from transmitter with a max length up to 65535 supported by

the embedded automatic packet handler.



CRC: can optionally be calculated on the transmitted data (PHR, MHR + MAC

Payload) and appended at the end of the payload (see Section 7.9: "CRC")



In the 802.5.4g the CRC, named FCS in the standard, is considered part of the PSDU

(PHY payload) hence the packet length, must include the 2 or 4 CRC bytes:



If the packet length programmed in PCKTLEN1 and PCKTLEN0 is L and CRC

mode is 3, then L-2 bytes will be read/written from/to the TX/RX FIFO and

interpreted as MHR + MAC Payload, 2 bytes CRC will automatically be calculated

and inserted at the end of the packet in transmission and stripped in reception.



If the packet length programmed in PCKTLEN1 and PCKTLEN0 is L and CRC

mode is 5, then L-4 bytes will be read/written from/to the TX/RX FIFO and

interpreted as MHR + MAC Payload, 4 bytes CRC will automatically be calculated

and inserted at the end of the packet in transmission and stripped in reception.



If CRC mode is 0, then L bytes will be read/written from/to the TX/RX FIFO and

interpreted as MHR + MAC Payload + MCS. In this case no CRC calculation,

insertion/stripping is done, and it is the responsibility of the MAC layer to process

it.

For CRC mode 3, according to the standard specifications, the CRC output is

complemented to 1 before transmission.

For CRC mode 5, if the payload length is less than 4 bytes then the payload is zero-padded

to reach a minimum length of 4 bytes. The padding bits are only used to compute the CRC

and are not transmitted on-air. The reverse operation is automatically performed on the

receiver.

7.4

UART over the air packet format

Table 53: UART over the air packet format

Preamble

Sync

Payload

0:2046 bits

0:32 bits

0:65535 bytes

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