L9678P datasheet(27/203 Pages) STMICROELECTRONICS

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L9678P, L9678P-S

Start-up power control

202

commands for squib driver switch tests will be ignored. Other checks are also performed: on

the arming output to check for non stuck-at conditions on the pin and for the configured firing

time. The SSM remains in this state until commanded to transition into the Safing state or

Scrap state via the dedicated SPI commands.

Upon reception of the SAFING_STATE command while in Diag state, the device enters

Safing state. This is the primary run-time state for normal operation, and the logic performs

the safing function, including monitoring of sensor data and setting of the ARM signal. The

only means of exiting Safing state is by the assertion of the SSM_Reset signal.

The Scrap state is entered upon reception of the SCRAP_STATE command while in Diag

state. While in Scrap state, the part allows the main microcontroller to initiate a transition to

Arming state, and monitoring of the Remote Sensor SPI interface (in L9678P-S) and the

safing logic is disabled. From Scrap state, the device can transition to Arming state only, and

the only means of moving back to Init state is through an SSM_Reset.

In order to protect from inadvertent entry into Arming state, and to prevent undesired

activation of the safing signals, a dedicated mechanism is used to control entry into, and exit

from Arming state. This mechanism is described further in Section 10.7: Additional

communication line. While in Arming state, the arming output is asserted. Exit from Arming

state occurs when the time-out is reached without a correct ACL signal or when SSM_Reset

is asserted. Upon exit, the device re-enters Scrap state, except for the case of SSM_Reset,

which results in entry into Init state.

System Operating states are shown in Figure 9.

Figure 9. System operating state diagram

L9678P Datasheet(PDF) 27 Page - STMicroelectronics