L9678P datasheet(147/203 Pages) STMICROELECTRONICS

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L9678P, L9678P-S

Safing logic

202

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).

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.



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

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 43.

In this example the ARM and dwell assignments for record1 only would be asserted.

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

state (refer to Figure 9). Additionally, the global bit to select internal or external safing

engine is set in Diag state.

10.3

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

Table 10. Records results comparison against two threshold

Combine Bit

Data

Resulting

Value

Record

Threshold

(assume ARMP)

ARMing Result

Record 1

Record 2

Record 3

Record 4

50 – 12 = 38

Record 1

12 + 50 = 62

Record 2

Record 3

12 + 50 = 62

Record 4

50 – 12 = 38

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