L9678P datasheet(134/215 Pages) STMICROELECTRONICS

134 / 215 page

Remote sensor interface

L9678P, L9678P-S

134/216

DS11626 Rev 9

A Manchester Decoder Error occurs if one or more of the following conditions 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.

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 with auto-adjust trip current

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

digital state (refer to Figure 35). Each satellite channel has a dedicated current sensor with

hysteresis.

Figure 35. Remote sensor current sensing auto adjust

The auto adjust feature uses a 7-bit D/A to converter to step up and down the threshold

level for detecting the base current through the remote sensor before start bits are

transmitted. Once start bits are received, the counter stops and the D/A value remains fixed

until the remote sensor message is received. This procedure is repeated for each cycle of

the remote sensor. The auto adjust circuit uses the following equation:

Ibase = Ioffset + (D/A counts) * 300 µA where Ioffset is fixed to 2.5 mA

GAPGPS01134

Isat

Ibase

Itri p

count

RxSat

0.5μs

e.g. 20mA

15mA

13mA

4μs

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