L9679P datasheet(177/272 Pages) STMICROELECTRONICS

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L9679P

Remote sensor interface

271

A Manchester Decoder Error occurs if one or more of the following are true:



Two valid start bits are detected, and at least one of the expected 13 mid-bit transitions

are not detected



Two valid start bits are detected, and more than 13 mid-bit transitions are detected



When the number of bits decoded is incorrect (either too many or too few), a bit error is

indicated. When any bit error is detected (bit time, too many bits, too few bits), the

decoder will revert to the minimum bit time of the selected range and the message is

discarded.

The Manchester decoder re-initializes at the start of each timeslot, such that remote sensor

frames violating timeslot boundaries will result in the setting of a Manchester Error. All errors

are readable through the Sensor Fault Status Register and the RSFLT bit in the Global

Status Word Register.

When a valid message is correctly decoded, the 10/8 data bits are stored into the

appropriate RSDRx register together with the related LCID. The RSDRx register contains

the 10/8 bits data as they are received from the sensor (no data range check/mask is done

at this stage). The 8-bit data word is right-justified inside the 10-bit data field in the RSDRx

registers.

Current sensor w/ auto-adjust trip current

The current sensor is responsible for translating the current drawn by the sensor into a

digital state. Each remote sensor channel has a dedicated current sensor.

The current flowing through the RSU power stage is internally downscaled by a factor 100,

sent to a 10 bits A/D converter and digitally processed to extract both the sensor quiescent

and delta currents.

The delta current threshold for signal detection can either be fixed or auto-adjusted to the

actual calculated sensor delta current, depending on the FIX_THRESH bit setting in the

RSCRx registers.

The current trip point is dynamically determined by adding the delta current threshold

(fixed/auto-adjusted) to the quiescent current (auto-adjusted). The RSU current is compared

against the current trip point to determine the current demodulator digital output. A logic '1'

represents the sensor current above the current trip point. The current demodulator output

is fed into the Manchester decoder and optionally to the WSx discrete output pins,

depending on the configuration of the RSPTEN bit in the RSCRx registers.

Thanks to the quiescent and delta current tracking features the receiver is capable to

automatically adapt to different nominal sensor currents and/or to be tolerant to sensor

current drifts over lifetime.

Both the sensor quiescent and delta current tracking algorithms can be configured by

setting appropriately the REDUCED_RANGE, BLOCK_CURR_IN_MSG and AVG/SSDIS

bits in the RSCRx registers.

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