L9678P datasheet(127/203 Pages) STMICROELECTRONICS

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L9678P, L9678P-S

Remote sensor interface

202

interface, subsequent requests for data from this channel will result in an error response

(NODATA fault).

The remote sensor interface is also able to detect faults occurring on the sensor interface.

The Remote Sensor Data Register (RSDRx) will report multiple fault flags.

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 or too few bits), the

message is discarded.

Error bit INVALID is an OR-ed combination of the following errors:



Data length error or stop bit error



Parity Error of received Remote sensor Message



Bit time error (a data bit edge is not received inside the expected time window)

Should one or more of the channel faults (STG, STB, CURRENT_HI, OPENDET and

RSTEMP) be set, the INVALID and NODATA bits are cleared.

7.1.2

RSU data fields and CRC

The remote sensor interface reports both data information and fault information in the

Remote Sensor Data Register (RSDRx). Independent data registers are defined for each

remote sensor interface and the data contained therein is formatted differently based on

whether a fault is detected. See SPI command in Remote sensor data/fault registers w/o

fault (RSDRx) on page 91.

The data available in the RSDRx register is separated into several bit fields. The Logical

Channel ID is a 4-bit field to identify the satellite sensor. The DATA bits are appended to the

LCID at the output of the Manchester decoder. The 3-bit CRC bit field is computed on the

entire data packet of fields, bits[16:0], which also includes the CHxON and FLTBIT. To

satisfy safety requirements, the LCID, DATA and CRC bit fields propagate through the same

data path as a single item to the SPI output.

The polynomial calculation implemented for PSI5 data is described as in PSI5 specification

g(x)=1+x+x^3 with the initialization value equal to "111".

Below are the equations to calculate the CRC in combinatorial way:

CRC[2] = CRCext[0]+D[0]+D[1]+D[3]+D[6]+D[7]+D[8]+D[10]+D[13]+D[14]+D[15]

CRC[1] = CRCext[2]+D[0]+D[1]+D[2]+D[4]+D[7]+D[8]+D[9]+D[11]+D[14]+D[15]+D[16]

CRC[0] = CRCext[1]+CRCext[0]+D[0]+D[2]+D[5]+D[6]+D[7]+D[9]+D[12]+D[13]+D[14]+D[16]

where D[16:0]= RSDR[16:0] and CRCext[n] are the starting seed values (all '1').

7.1.3

Detailed description

Manchester decoding

The Manchester decoder will support remote sensor communication as per PSI

specification rev 1.3 for the modes configurable via the STS bits in the RSCRx registers.

The Manchester Decoder checks the duty-cycle and period of the start bits to determine

their validity, depending on the configuration of the PERIOD_MEAS_DISABLE bit in the

RSCRx registers. The expected time windows for the mid bit transitions of each subsequent

bit within the received frame is determined by means of the internal oscillator time base.

Glitches shorter than 25% of the minimum bit time duration are rejected.

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