S2-LP datasheet(53/90 Pages) STMICROELECTRONICS

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S2-LP

Packet handler engine

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7.2

STack packet

Table 50: STack packet

Preamble

Sync

Length

Dest.

address

Src

address

Seq

num

NO_ACK

Payload

CRC

Postamble

0:2046

bits

0:32

bits

0:2

bytes

1 bytes

bits

1 bit

0:65535

bytes

0:4

bytes

0:510 bits



Preamble: each preamble is a

pair of ‘01’ or ‘10’ from 0 pair to 2046 pairs,

programmed by the register PREAMBLE_LENGTH. The binary sequences transmitted

in the various modulation modes are summarized in Table 49: "Preamble field

selection" (leftmost bit is transmitted first).



Sync: the pattern that identify the start of the frame can be configured in value with a

programmable length from 0 to 32 bits, in steps of 1-bit length. The setting is done by

the register SYNC_LENGTH. The S2LP supports dual synchronization with a either a

primary or a secondary synchronization word. The binary content of the primary SYNC

word is programmable through registers SYNCx (x= 1, 2, 3, 4). The binary content of

the secondary SYNC word is programmable through registers SEC_SYNCx (x= 1, 2,

3, 4), note that such registers are in alternate use with address filtering registers. On

the transmitter side either the primary or the secondary word is transmitted according

to the value of the SECONDARY_SYNC_SEL register, in particular if

SECONDARY_SYNC_SEL = 0 then the primary synchronization word is transmitted;

if SECONDARY_SYNC_SEL = 1 then the secondary synchronization word is

transmitted. On the receiver side, the primary synchronization word is always enabled.

The search for the secondary synchronization word can be enabled setting

SECONDARY_SYNC_SEL = 1b. In this case, both the binary patterns are searched

for and both of them can trigger the start of payload demodulation. The SQI[5:0] value

reported in the LINK_QUALIF register is the maximum between the SQI of the primary

and secondary words. The bit SQI[6] indicates which synchronization word has been

detected: in particular, if the secondary synchronization word has been detected then

the SQI[6] = 1 otherwise if the primary synchronization word has been detected then

SQI[6] = 0. The binary pattern programmed in SYNCx (or SEC_SYNCx) is transmitted

on air starting with the most significant bit of x = 1, to the least significant bit of x = 4

according to the programmed synchronization word length.



Length: The device supports both fixed and variable packet length transmission from

0 to 65535 bytes. On the transmitting device, the packet length is always set by using

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

receiving device, if FIX_VAR_LEN register is set to ‘1’, the packet length is directly

extracted from the field Length of the received packet itself. If the register

FIX_VAR_LEN = 0b the Length field of the received packet is not used, because is

already known from the registers PCKTLENx (x= 1, 2) as for the transmitter.

Furthermore, when variable packet length is used (FIX_VAR_LEN=1b), the width of

the binary field transmitted, must be configured through the LEN_WID register in the

following way:



If the packet length is from 0 to 255 bytes (payload + address field), then

LEN_WID = 0 (1 byte length field transmitted).



If the packet length is from 0 to 65535 bytes (payload + address field), then

LEN_WID = 1 (2 bytes length field transmitted).



Destination address: the receiver uses this field to perform automatic filtering on its

value. It is a mandatory field always on. The destination address field is read from the



Source address: the receiver uses this field to perform automatic filtering on its value.

It is a mandatory field always on. The source address field is read from the register

TX_SOURCE_ADDR (TX only).

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