L9680 datasheet(204/277 Pages) STMICROELECTRONICS

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Safing logic

L9680

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DocID029257 Rev 1

Comb (Combined Data) bit allows combining X and Y for off-axis oriented sensors. In this

case, it is typical for such orientations to add or subtract the sensor response to translate the

sensor signal to an on-axis response. Only couples of 16-bit long records have this feature

(i.e. 1&2, 3&4, 5&6, 7&8, 9&10, 11&12).

Records are added and subtracted and results compare against two thresholds. Safing

engine will process data as follows:



Use record(n) and record(n+1), where n = 1, 3, 5, 7, 9, 11.



The matching inputs used for math combinations are processed only after both are

captured.



The sum of the two matching inputs will be compared to the threshold of record(n).



The difference of the two records will be compared to the threshold of record(n+1).



If the Comb feature was enabled on only one of the two records in a couple, math

would be performed only on it as shown in Figure 55

Example of Combine Function operation:

All items in the safing records, except En(Record Enable) bit, can be configured only in Diag

state (refer to Figure 10). Additionally, the global bit to select internal or external safing

engine is set in Init state.

12.3

In-frame and out-of-frame responses

Some sensors will communicate data within the current communication frame while others

will send data on the next communication frame. Sometimes this is sensor specific and

sometimes this is due to the amount of data to be transmitted. A simplified diagram shows

the basic communication differences of in and out of frame responses.

In-frame example:

Table 15. Example of combine function operation

Record #

Combine

Bit

Data

Resulting value

Record

Threshold

ARMSELx

Configuration

ARMINTx

Result

Record 1

ARMP

Record 2

ARMP

Record 3

ARMP

Record 4

50 – 12 = 38

ARMP

Record 5

12 + 50 = 62

ARMP

Record 6

ARMP

Record 7

12 + 50 = 62

ARMP

Record 8

50 – 12 = 38

ARMP

Record 9

50 + 12 = 62

-24

ARMN

Record 10

12 – 50 = -38

-24

ARMN

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