S2-LPS datasheet(40/73 Pages) STMICROELECTRONICS

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6.3

Wireless MBUS packet (W-MBUS, EN13757-4)

The W-MBUS packet structure referred to EN13757 can be obtained through registers setting programming the

basic packet to fit the specific sub-mode used.

Preamble

Sync

1st block

2nd block

Opt. blocks

Postamble

Preamble: the preamble is fully programmable to fit the W-MBUS protocol. The generic setting is a pair of ‘01’ or

‘10’ from 1 pair to 1024 pairs (max. 256 bytes).

Sync: the pattern that identify the start of the frame is fully programmable to fit the W-MBUS protocol. The generic

setting is in value with a programmable length from 1 bit to 64 bytes, in steps of 1-bit length.

Data blocks: the data coding can be fully programmed in NRZ and Manchester.

Postamble: The packet postamble allows inserting a certain number of ‘01’ bit pairs at the end of the data packet.

The number of postamble bit pairs can be set through the MBUS_PSTMBL register depending on the chosen

sub-mode according to the W-MBUS protocol.

6.4

Payload transmission order

The bit order of the data from TX FIFO and written into the RX FIFO is controlled by the BYTE_SWAP register. In

particular, the transmission is MSB first if BYTE_SWAP = 0 and LSB first if BYTE_SWAP = 1.

6.5

Automatic packet filtering

The receiver uses the following filtering criteria to reject the received packet. The automatic filtering is supported

in BASIC and STack packet format only.

•

CRC: the received packet is discarded if CRC check fails. Both transmitter and receiver must be configured

with same CRC polynomial.

•

Destination address vs my address: the received packet is discarded if the destination address field

received does not match the programmed my address of the receiver.

•

Destination address vs. broadcast address: the received packet is discarded if the destination address

field received does not match the programmed broadcast address of the receiver.

•

Destination address vs. multicast address: the received packet is discarded if the destination address

field received does not match the programmed multicast address of the receiver.

•

Source address: the received packet is discarded if the source address received does not match the

programmed source address reference (a bit mask can be included). Supported in STack packet format only.

The automatic filtering can be programmed to discard packet below certain threshold settings. These kind of

filtering are general purpose and can be used with any packet format.

•

Carrier sense: The carrier sense (CS) functionality detects if any signal is being received, the detection is

based on the measured RSSI value. There are 2 operational modes for carrier sensing: static and dynamic.

In static CS mode, the CS is high when the measured RSSI is above the RSSI threshold specified and is

low when the RSSI is 3 dB below the threshold. In dynamic CS mode, the CS is high if the signal is above

the threshold and a fast power increase of 6, 12, or 18 dB is detected. The CS is also used internally for the

demodulator to start the AFC and timing recovery algorithms (static CS mode only).

•

PQI: It is possible to set a PQI threshold in such a way that, if PQI is below the threshold, the packet

demodulation is automatically aborted.

•

SQI: It is possible to set a SQI threshold in such a way that, if SQI is below the threshold, the packet

demodulation is automatically aborted. When the SQI threshold is set at 0, a perfect match is required. It is

recommended to always enable the SQI check.

6.5.1

CRC

Error detection is implemented by means of cyclic redundancy check codes. The CRC is calculated over all fields

excluding preamble and SYNC word. The length of the checksum is programmable to 8, 16, 24 or 32 bits. The

following standard CRC polynomials can be selected:

•

mode 1: 8 bits: the poly is (0x07) X8+X2+X+1

S2-LPS

Wireless MBUS packet (W-MBUS, EN13757-4)

DS13831 - Rev 1

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