S2-LP datasheet(67/90 Pages) STMICROELECTRONICS

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S2-LP

Link layer protocol

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67/90

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If the CS valid is low, then the RX is aborted immediately.



If the CS valid is high, then the RX continues and the main controller starts the

CS/PQI/SQI timeout mechanism programmed.

The typical application scenario of the feature described above is the asynchronous LDC.

More specifically, if receiver and transmitter are not synchronized, then the receiver has to

‘sniff’ about the presence of a carrier during most of the wake-up time slot (inside the

preamble transmission) and, in case of carrier level above the programmed threshold (CS

valid), to wait for the SYNC word after the preamble.

If the carrier is not present, the receiver should go back to sleep as soon as possible

without waiting furthermore, in order to save on average current consumption.

Figure 17: Fast RX termination mode with LDC

If the carrier is present, it will be possible to receive the entire frame because the RX

timeout stop condition is switched to the normal mechanism of PQI/SQI and SYNC can be

detected:

Figure 18: Fast Rx termination: CS detection

In order to ensure that TX frame is always captured, it is advisable to set wake-up time to

less than the preamble time.

8.3

CSMA/CA engine

The CSMA/CA engine is a channel access mechanism based on the rule of sensing the

channel before transmitting (listen before talk). This avoids the simultaneous use of the

channel by different transmitters and increases the probability of correct reception of data

being transmitted. This is done by a comparison of the RSSI sensed with the

S2-LP Datasheet(PDF) 67 Page - STMicroelectronics