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SMJ320F2812: Unused pins + Emulation

Hi team,
We have a couple of questions from one of our customers, VSSC. Can you please help with the answer?
1. We are not using some of the F2812 pins for example XA, XD, TCLKIN and C3TRIP. What exactly will happen to the DSC if these pins are shorted to ground?
2. I need to simulate my application code in code composer studio without connecting to the target/emulator. Is it possible?

  • Hi
    This question is regarding the unused ADC block in the F2812 referring to post e2e.ti.com/.../523106.
    I read in the app note that the ADCREFP and ADCREFM should be tied to ground using 2.2uF even when the ADC block is unused. Is there a reason why we advise against floating these pins? If it can be floated without any adverse effect, it will reduce component count on the board.
    Can we float the ADCRESEXT pin too instead of using a 22k resistor to ground?
  • Hi Mahesh,

    I was unable to follow the link you provided, but you should follow the recommendations found in section 3.4.2.5 ADC Connections if the ADC is Not Used of Hardware Design Guidelines for TMS320F28xx and TMS320F28xxx DSCs.  That is to say the capacitors on REFP/REFM can be reduced from 2.2uF to 100nF but yes the resister on RESEXT should remain at DS specified value.  This was determined to be the safest approach when the ADC is not used.

    Regards,

    Joe

  • On 2812, the XINTF pins are not multiplexed with GPIO function. Since XAn are (and XDn could be) output pins, one should not short them to GND. If an XINTF access was erroneously attempted, damage may ensue at the pins as there would be no resistance to limit the output current directly into ground. The internal pullup on XD is adequate in simple situations. However, in noisy environments, an external pullup on each of the XD pins should be considered. The XA pins are outputs with a reset value of “0” and could be left in that state. The XREADY pin should have an external pull-up. The -XHOLD pin should have an external pull-up as well to ensure the XINTF bus is not put into high impedance. External pull-ups should be on the order of 1k-ohm to balance noise immunity and a limit to fault current.

    Regarding TCLKIN & C3TRIP, in general, it is not a good idea to short GPIO pins directly to GND. This is to prevent these pins from being configured as outputs and driven inadvertently. So, a series resistor is preferred.

    As a general comment, it is hard to predict from our end all the perturbations the system would be subjected to. So, the onus is on the customer to rigorously test the solutions proposed to ensure their design is robust.