L9679P datasheet(201/279 Pages) STMICROELECTRONICS

201 / 279 page

DS11627 Rev 7

201/279

L9679P

Safing logic

278

POS_COUNT and NEG_COUNT are not updated if microcontroller stops reading SAF_CC

bits (this must be avoided otherwise ARMING set and reset will not be possible).

By way of the assignment of the ADD_VAL, SUB_VAL, ARMP_TH and ARMN_TH settings,

the safing engine can be configured to assert arming for either a simple accumulation of

COUNTs in a non-consecutive manner, or it could be set to require some number of

consecutive samples.

12.5

Safing engine output logic (ARMxINT)

SPI messages are monitored and mapped to specific safing records. Each safing record is

configured with its own threshold, dwell time and the appropriate ARMxINT signal to

activate if safing criteria are met.

Any enabled safing record can be programmed to an arming signal. All safing records

arming status is logically ‘OR'd’ to its programmed arming signal. For example, if safing

records 1, 2, 4 are programmed to ARMINT1 and the records are enabled, any of the

records can set the ARMINT1 signal. Configuration of safing record mapping to ARMxINT

signals is specified in the SAF_CONTROL_x register (refer to Table 66).

While in Diag state, L9679P allows diagnostics of the squib/pyroswitch driver HS and LS

FETs, ARM pins, VSF output and firing timers. The ARM and VSF output tests are mutually

exclusive.

For safety purposes, the safing logic circuitry is physically separated from the circuitry that

contains the deployment logic.

L9679P Datasheet(PDF) 201 Page - STMicroelectronics