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TMS570LC4357: Does TMS570LC4357 support analog loopback mode for every Pin?

Max Wittekind
Expert 1895 points

Part Number: TMS570LC4357

Hello Experts,

The Safety Manual mentions the Diagnostic GIO1A "Boot Time Software Test of Function Using I/O Checking In GIO Mode" which mentions that the I/O in GIO Mode can be tested with an analog loopback diagnostic. I know that Modules like SPI or Flexray have a digital and analog loopback mode. But I could not find anything on loopback mode of the GIO Pins.

(Q1) Is the analog loopback mode implemented for every Pin of the µC or just a few modules (e.g. SPI)? If this is the case, where can I finde the necessary configurations?

Additionaly im not completly clear on how the analog and digital loopback work. As far as I understand, the digital and analog loopback mode test the same functionality but analog mode includes the outputdriver. This would mean that setting a Pin to high in analog loopback mode would also influence the circuit outside of the µC.

(Q2) Is my understanding correct?

Thank you and best regards,
Max

  • 0
    TI__Guru**** 200206 points

    Hello,

    Many of the modules can operate in their functional mode or GIO mode. When in GIO mode it means you can use their functional pins in General Purpose Input/Output. You can simply control these I/O pins by writing/reading these pins directly. Not all the modules can be configured to GIO mode: ADC, EMIF etc.

    Please refer to the description column of the terminal function tables in section 4.2 of device datasheet.

    Your understanding is correct. Analog loop back will include the input and output buffers while the digital loop back will not. The digital loopback is done inside the chip bypassing the input/output buffers. This is the biggest difference. If you choose the analog loopback you will also exercise and test the I/O buffers. Let's say if the I/O buffer is bad, then a analog loopback test will detect the fault. However, it depends on how is the MCU is connected to the rest of the devices on your devices. In an analog loopback test if you are driving a signal to an I/O where this I/O is connected and also being driven by another device on the board then you will have a driving conflict. Doing a digital loopback as stated is done inside the chip excluding the I/O path and will not have the problem. 

  • 0 in reply to QJ Wang
    Expert 1895 points

    Hello QJ,

    thank you for answering my question. I have two follow up question:

    (Q3) The documentation does not seem clear, about the state of the Pins that are tested with the digital loopback mode. For example, if I want to test Pin 0 with Pin 1 and Pin 0 is Output High before the switch to digital loopback mode, will Pin 0 still be Output High although I am switching the Pin internaly?

    (Q4) As far as I can tell from the documentation digital loopback mode is only avaible for Ethernet, Flexray, MibSPI, N2HET, I2C,SCI, LIN,CAN. Is that correct?

    Thank you and best regards,
    Max

  • 0 in reply to Max Wittekind
    TI__Guru**** 200206 points

    Hi Max,

    Apologizes for late response. The following are my comments:

    Max Wittekind said:
    (Q3) The documentation does not seem clear, about the state of the Pins that are tested with the digital loopback mode. For example, if I want to test Pin 0 with Pin 1 and Pin 0 is Output High before the switch to digital loopback mode, will Pin 0 still be Output High although I am switching the Pin internaly?

    Yes, the value will not change. For example, mibSPI T X RAM is programmed before the loopback is enabled, after loopback is enabled, the data in TX RAM will not change.

    Max Wittekind said:
    (Q4) As far as I can tell from the documentation digital loopback mode is only avaible for Ethernet, Flexray, MibSPI, N2HET, I2C,SCI, LIN,CAN. Is that correct?

    Yes, you are correct.