TMS570LS3137: What is Monitoring by Second N2HET ?

Arriy,

Monitoring by use of HET2 is basically using the second HET (HET2) module on the device to receive the output from HET1 as an input channel and analyze the input signal to ensure integrity of the output of HET1. This mechanism would be done only by hard wiring a HET1 output to a HET2 input. Unique HET1 and HET2 programs would need to be written to realize the monitoring operation. For example, if HET1 were used to output a 1KHz PWM at a 50% duty cycle, it could be also wired/connected to a HET2 channel which could use input capture to measure the pulse widths and insure that the 1KHz frequency was maintained and that pulses were provide such that the 50% duty cycle is maintained. This mechanism would have to be designed and coded specific to the application needs.

Software test of function using I/O loopback is different in that it uses the loopback capability of the module to insure proper operation of the logic and doesn't require any special wiring on the PCB. More information can be found in the NHET chapter of the technical reference manual that describes the various options for loopback available for the NHET module.

Hello Chuck.
Thank you for your answer.

> This mechanism would be done only by hard wiring a HET1 output to a HET2 input.
You said, to realize the safety mechanism(7.88 Monitoring by Second N2HET) need to HW wiring.

But,Safety Manual(SPNU511D) it is explained as "The N2HET supports an internal channel connection between the two N2HET modules to facilitate easy monitoring of one N2HET by a second N2HET." and "Alternatively external connections can be used.".

Which one is correct ?

Best Regards.

Hello Arriy,

This is dependent on which channels/pins are used for the NHET functionality. Below is a snippet from the LS3137 datasheet that shows the configuration of the channel's buffers when they share the same pin through the pin mux feature. You will notice that the output is muxed while the inputs are connected. So, if you use the default N2HET1 function on the pin, the input will go to both the N2HET1 input buffer and the N2HET2 input buffer. Because of this, you would not be required to use any external wiring to realize the shared input/monitoring loop. If you don't use one of the shared pins, then you would need external wiring.

Hello Chuck.

Thank you for your advice.I'm slowly starting to understand.

N2HET1[1] and N2HET2[8] is internal connected,would not need external wiring.

But for example, if I want to loopback of N2HET1[2] or N2HET2[1], then I would need external wiring.

This recognize is right?

So I have more two questions. (Q1) If I would need external wiring, what kind of external wiring ? Simply connect ?

(Q2) I confirmed "HET1" and "HET2" tab in HalCoGen again. HET1 and HET2 have number of pin is not match(HET1 = Pin0~31 , HET2 = Pin0~18).

Why do not they match ?  What should I do if I want to loopback HET1 pins that do not correspond to HET 2 ?

Best Regards

Hello Arriy,

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