L9396 datasheet(46/109 Pages) STMICROELECTRONICS

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Remote sensor interface

L9396

46/109

DS12539 Rev 6

5.1.1

Wheel speed data register formats

In the wheel speed sensor interface four data registers are used (Remote Sensor Data

Independent data registers are defined for each wheel speed channel and their contents are

determined by sensor type. Three-level VDA sensors have eight data bits and parity as

shown in the table below. At fast speed not all bits may be transmitted by the sensor: the IC

is able both to process normal or either truncated frames by providing together with data, a

4-bit counter to inform the microcontroller about the number of received valid bits.

For PWM encoded sensors, each pulse length is written to the sensor data register with a

typical resolution of 5 µs per bit. In case of pulse width duration equal to or higher than

1.045 ms, the standstill condition will be recognized and bit 15 in the corresponding register

will be set.

The register is updated when a PWM falling edge is detected; in case of stuck-at 1 of the

PWM signal the register is updated when the counter reaches the overflow value (0x1FF): in

this case the standstill bit not set and the counter in overflow will signal a fault to the

microcontroller.

5.1.2

Testmode

In order to test the input structures of the connected microcontroller, the device features a

wheel speed test mode that allows test patterns to be applied on the four wheel speed

outputs WSOx. The test mode can be entered via SPI and the test patterns can also be

controlled via SPI commands. Test patterns can be composed only of static high or low

signals, which can be selected via SPI. For safety reasons only one channel at a time can

be switched into test mode.

In order to enable testmode it is necessary to write to '1' bit DIAG (bit 4) of register

RS_CTRL. After that the bits of WSS_TEST register select the channel under test and the

state of output pin.

To exit this testmode it is not sufficient to clear to '0' the DIAG bit but, before that, also bits

8:2 of WSS_TEST register (Config range field) must be changed in order not to select any of

the four available outputs.

5.1.3

Wheel Speed SPI Registers

WSI test

WSS_TEST register stores Static Test configurator bit-field.

This register configures a static test for WSI interface. Test consists in transferring TestBit

value on a selected (by Config range) WSI output.

TestBit: Test input value.

Table 20. WSS_TEST register

Addr

Name

Type

Bits = 9

0001111

WSS_TEST

Config Range= 8:2, X:1, TestBit = 0;

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