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N2HET[n]/N2Het[n+1] Loopback Impact on different periphery interfaces

Krax
Prodigy 130 points
Part Number: RM44L920

Hello,

I have a question about the N2HET loopback function as it couples 2 HR structures to run a test over the digital or analog path. 
If I do this, can I use the loopback function in simple GIO mode or is the N2HET structure expecting a PWM signal which is feed to the neigbour HR structure?

According to the TRM for the HETLBPSEL and HETLBPDIR registers, it states that "The pin which is not driven by the N2HET pin actions can still be used as normal GIO pin." - does that mean when I want to apply the test in GIO mode on the N2HET pins that the corresponding neighbour pin ( n+1) of the N2HET loopback pair which is used in a serial communiction context to provide for example a clocking signal stops to work? This pin can only be used in normal GIO mode instead, alternative functions derived from a different interface are not taken into account anymore when applying the test ?

  • 0
    TI__Guru**** 197036 points

    The N2HET loopback can not be used for GIO mode. When loopback is used, the (n+1) HR structure is used to monitor the PWM period and duty cycle generated by (n) HR structure. 

    The (n+1) N2HET structure expects the PWM signal which is generated by (n) N2HET HR structure.

  • 0 in reply to QJ Wang
    Prodigy 130 points

    Hello QJ Wang,

    thanks for your feedback. Understood. If I use such a loopback test on the (n) and (n+1) N2HET structure, does the corresponding N2HET pin (n) which is maybe used to generate a clock signal in our application for example SCI, SPI, etc is still useable when the test is active? If not, when I recover all the backup N2HET registers after a successful test and I deactivate the Loopback test, does it still impact the alternative functionality of the pin which was thought to be used in a different context e.g. SPI clock, etc ?

  • 0 in reply to Krax
    TI__Guru**** 197036 points
    Krax said:
    If I use such a loopback test on the (n) and (n+1) N2HET structure, does the corresponding N2HET pin (n) which is maybe used to generate a clock signal in our application for example SCI, SPI, etc is still useable when the test is active?

    No. 

    Krax said:
    If not, when I recover all the backup N2HET registers after a successful test and I deactivate the Loopback test, does it still impact the alternative functionality of the pin which was thought to be used in a different context e.g. SPI clock, etc ?

    You need to re-configure the Pinmux to use the pin for SPI or SC, etc.

  • 0 in reply to QJ Wang
    Prodigy 130 points

    thanks for your reply. If I finish the loopback test and I restore all the backup registers including the pinmux register, do I need to re-initialize the SCI or SPI Init again to use that serial communication interface properly, just in case the system was already initialized into a defined state before the loopback test was conducted?

  • +1 in reply to Krax
    TI__Guru**** 197036 points

    I don't think you need to re-initialize SPI again.