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TMS570LC4357: nError signal and self test compatibility

Jiri Dobry
Expert 1810 points
Part Number: TMS570LC4357

Hello

we have problem with nError ping behavior during self tests.

In SPNS195C chapter 6.19 Error Signaling Module we found this information: "The nERROR can be used as an indicator to an external monitor circuit to put the system into a safe state."

OK, we are using this signal to put rest of system to "safe state". We are able to test ESM unit and this signal connection during boot (system is on safe state for booting). This signal can't be activated during normal operation later.

Problem is conflict with safety manual. For example SPNU540A chapter 7.133 Software Test of Parity Logic test ID "RAM13"  (Table 4. Summary of Safety Features and Diagnostics) is marked as "Periodic / On-Demand". Problem is that this test can't be periodic, because this test activate nError signal every time. Is it correct? Can you clarify it?

Jiri

  • 0
    TI__Mastermind 49120 points
    Hello Jiri,

    The nERROR pin is expected to toggle during several self-test of several diagnostic mechanisms. There is even a diagnostic check for the nERROR pin itself. Some applications have a communication method between the MCU and the safety monitor to indicate that the MCU is running self-tests on diagnostic mechanisms. Then the safety monitor would ignore a low-state on the nERROR pin. There is also a way to control the duration for which the nERROR pin is driven low for every error condition. This is managed via the ESM Low-Time Counter Preload Register (ESMLTCPR). The application can configure different preload values for diagnostic self-tests versus normal operation. The safety monitor then needs to identify whether the nERROR is asserted because of a diagnostic self-test or whether it is a real error condition.

    Regards,
    Sunil