L9679E datasheet(89/127 Pages) STMICROELECTRONICS

89 / 127 page

System voltage diagnostics

L9679E has an integrated dedicated circuitry to provide diagnostic feedback and processing of several inputs.

These inputs are addressed with an internal analog multiplexer and just one internal ADC and made available

through the SPI digital interface with the diagnostics data commands. In order to avoid saturation of high-voltage

internal signals, an internal voltage divider is used. The diagnostics circuitry is activated by four SPI diagnostics

control commands (DIAGCTRLx); each of them can address all the available nodes to be monitored, except for

what mentioned in Table 14. Diagnostics control register (DIAGCTRLx).

The DIAGCTRLx SPI command bit fields are structured in the following way:

DIAGCTRL_A (ADDRESS HEX 3A)

MOSI

ADCREQ_A [6:0]

MISO

NEWDATA_A

ADCREQ_A[6:0]

ADCRES_A[9:0]

DIAGCTRL_B (ADDRESS HEX 3B)

MOSI

ADCREQ_B [6:0]

MISO

NEWDATA_B

ADCREQ_B [6:0]

ADCRES_B [9:0]

DIAGCTRL_C (ADDRESS HEX 3C)

MOSI

ADCREQ_C [6:0]

MISO

NEWDATA_C

ADCREQ_C [6:0]

ADCRES_C [9:0]

DIAGCTRL_D (ADDRESS HEX 3D)

2 1

MOSI

ADCREQ_D [6:0]

MISO

NEWDATA_D

ADCREQ_D [6:0]

ADCRES_D [9:0]

ADCREQ[A-D] bit fields, used to address the different measurements offered, are listed in Table 14. Diagnostics

control register (DIAGCTRLx) for reference.

L9679E diagnostics is structured to take four automatic conversions at a time. In order to get four measurements,

four different SPI commands have to be sent (DIAGCTRL_A, DIAGCTRL_B, DIAGCTRL_C and DIAGCTRL_D) in

no particular order.

In case the voltage to be measured is not immediately available, the desired inputs for conversion have to be

programmed by SPI in advance, to allow them to attain a stable voltage value. This case applies to the squib/

pyroswitch resistance measurement and diagnostics (refer to Squib/Pyroswitch diagnostic with common SRx

connected loops).

CONVRDY_0 bit in GSW is equal to (NEWDATA_A or NEWDATA_B), while CONVRDY_1 bit in GSW

corresponds to (NEWDATA_C or NEWDATA_D).

Each NEWDATAx flag is asserted when conversion is finished and cleared when result is read out. However, the

result is cleared only when a new result for that register is available.

When a new request is received, it is queued if other conversions are ongoing. The conversions are executed in

the same order as their request arrived. The queue is 4 measures long so it is possible to send all 4 requests at

the same time and then wait for the results. If a DIAGCTLRx command is received twice, the second conversion

request will overwrite the previous one.

L9679E

System voltage diagnostics

DS12485 - Rev 8

page 89/127

L9679E Datasheet(PDF) 89 Page - STMicroelectronics

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