Member Orunmila Posted February 24, 2019 Member Share Posted February 24, 2019 I am trying to configure the DAC on the 47K40 Xpress Evaluation board using MCC and I am confused about what I see. The screen I see is to the right -> I can understand that the Vref+ and Vref- fields are necessary when you are using the input pins for a reference but it is really confusing when the Vref+ is shown and it is read-only AND it shows an incorrect value as it does here. I would have expected that if I select Vdd as the reference the Vref+ value would either be hidden, or that it would have the same value as Vdd. I also do not understand why the Output of the DAC is referred to as "Required ref", this talk of "Ref" all over the place is very confusing to the unsuspecting user. You should call the DAC out Value the Required DAC out Value above the line you show the result of the calculation, and when the references are set to Vdd or Vss then Vdd should match Vref+ and Vref- should be 0 even if those are read-only - even better just hide them if they should not be used! It turns out that Vref+ and Vref- are ignored if you have selected Vdd and Vss, and that Required Ref actually means the output that you desire to get from the DAC, for those as confused as I was. When you select the Vref+ pin as the reference then Vdd field is ignored. It also seems that the Vdd and Vref+ fields allow you to enter values way outside the electrical specs of the device, it does create a note that this is the case, but I would have expected a proper warning for something dangerous like this, at first I did not even notice this as it was green and just a note. Lastly when I select to use the FVR _buf2 as the positive reference for the DAC the screen no longer makes any sense. Now I can only edit Vdd (which is 5v) but my Vref is set to 2.048V via the 2x buffer on the FVR, but the Vref+ field is read-only so I cannot update it. MCC is however using the correct input reference of 2.048 as can be seen by the output being limited to 1.984V even when I require 3V. Required Boilerplate: Component Version Device PIC18F74K40 MCC 3.75 MPLAB-X 5.10 Foundation Services 0.1.31 PIC18 Lib 1.76.0 Quote Link to comment Share on other sites More sharing options...
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