CCS/TMS320F28027: TMS320F28027

Hi,

I am getting waveform of 50Hz,but when i try to sense  triangular waveform of 200KHz frequency with DC offset and pass it to ADC pin A7  .I set the count of 30 for sampling rate of 0.5us,but was unable to get the waveform in graph .For my application i need to sense 4 ADC signal of 200KHz.I have attached the graph  of ADC example.

Regards,

Kalpesh

Kalpesh Kolhe said:

I set the count of 30 for sampling rate of 0.5us,but was unable to get the waveform in graph

Graph has an update rate of at the max 100ms which is not recommended. 200ms update rate is more stable! Hence don't expect the graph tool to draw a us signal. Do check the ADCResult registers under ADCRegs to compare the inputs values with the digital values.

Regards,

Gautam

Hi,
In what form are value stored in graph and one in ADC result register and how can i convert this digital value to my original analog value.I referred the ADC calculation in ADC Guide.Can u provide me with a calculation example.

Regards,
Kalpesh

The above graph that you're plotting is ADC in digital counts or what you observe in ADCResult registers. If you need to convert the same in to analog, you need to do this calculation: (x/4096)*3.3 ; where x = 12-bit ADC value in digital counts

Hi,
Then to sense a signal of some frequency which parameter should i change in ADC program if its not using ePWM value.

I need sampled values for further comparison. So i just need to know how to sense a 200kHz wave and store it in a buffer.

Thank You.

Regards,

Kalpesh

Kalpesh Kolhe said:

So i just need to know how to sense a 200kHz wave and store it in a buffer.

You're already sensing the signal on ADC right? That's why I asked you whether you require the peak value or an average value of the triangular wave.

Yes I am getting instantaneous value,but they are not correct.My objective is to sense the signal given to ADC pin through function generator and display it in graph window. Which parameter should i change for changing sampling rate in ADC_SOC example using ePWM.

Hi,
That's what i need to know ,I was applying the logic that for sampling 200kHz triangular wave with a sampling rate of 0.5us the count in ePWM should be change.The result were wrong.So i want to understand the correct method or calculation to sample the 200kHz .I am referring the ADC_SOC example .

You can find the formula to calculate ePWM frequency from TBPRD value here: e2e.ti.com/.../1398914

Kalpesh Kolhe said:

And what will be the CMPA value? If TBPRD value determines the ADC sampling rate.

Kalpesh, you need to go through User guides properly. All these questions of yours are very well explained! Secondly, I've previously very well mentioned that Graph utility cannot plot high frequency signals... it has a refresh rate of 500ms -  2Hz (default) and can be tweaked to 100ms - 10Hz..

I would suggest you to please read the ADC, ePWM user guides thoroughly!

Regards,

Gautam