ADC trigger from HET on eval board

Hi Chris,

First let me apologize for the length of time it has taken us to respond to you.  We obviously missed our 24 hour response/acknowledgement goal.

The ADC can be triggered in two ways: generating the trigger timing from the on-chip HET or by using the ADEVT (pin 68) on the chip.  Since you are using the USB evaluation board, unfortunately, you won't have direct access to this pin from a header or test point.  I don't think you'll have to remove an LED but I do believe that you would have to get out the soldering iron and attach a blue wire directly to pin 68.  

I will ask the board designer if he has any other ideas on how best to externally trigger the ADC.

Chris Smith said:

Hi, I'm trying to evaluate the ADC configuration and performance on the TMS470M USB Development Stick.  In the datasheet I can see that the ADC hardware trigger sources are HET 1, 3, 16, 18, 24, 26, 28.  On the eval board 1 and 3 are tied to LEDs as outputs and the HET pins stop at 15.  The datasheet does mention that "These channels are available as internal signals"  What does that mean?  Is there a way to use another pin and somehow internally tie it to a HET channel?

HW: Let me give an example. HET 28 is not available on the package, but it presents in the HET module inside the device. You can still drive a PWM waveform or rising/falling edge on this 'pad' to trigger the ADC. The ADC read the rising/falling edge inside the device even if it does not present on the 100 pins. In the motor control application, for example, HET0-5 are used to generate PWM to drive motor, HET 28 can be used to generate PWM to trigger the ADC to save one IO. Am I clear?

I've used the HAL tool for HET configuration so far and it doesn't seem to have much detail there. 

If I can't "re-map" the het channels how do I bring in a hardware trigger for my ADC?  Get out the soldering iron and remove an LED?

HW: if you plan to  trigger ADC from external signal, ADEVT, HET1 and HET3 are the only choice. In the USB stick, connecting the external signal to HET1,3 LED (close to the MCU side) might be the best solution (you don't have to remove LED if the external signal can drive more than 2mA current. But you need to make sure that HET1 or 3 is configured as input).

Thanks,

Chris

HW, I understand what you mean about the HET signals higher than 15 can be internally generated and used, but it seems there is no way to take an input pin and have it processed by the extra (higher number) HET channels? 

I've connected my input signal to the existing HET3 LED and it works well.  I was thinking the LED would pull more current but I guess not.

Thanks for the help,

Chris