ADC values in graph- F28335- CCS4

Mahesh Venugopal

Other Parts Discussed in Thread: TMS320F28335

Hello!

I have done an ADC coding for TMS320F28335 in code composer studio4.It is working fine.The values corresponding to analog signal is getting stored in corresponding registers.

Now i want to input a sine wave and see the corresponding digital values in a graph.

Before that i saw the graph when ADC pins are grounded.I expected a graph in which values are zero or near to zero.But the obtained graph was this:

What is the actual problem?

It would be great if any one can solve this problem.

regards

Mahesh

over 12 years ago

0 Devin Cottier over 12 years ago

TI__Guru 60865 points

Hi Mahesh,

I am not sure how to interpret the vertical scale on your graph, can you show it in the range of raw ADC conversions: 0 to 4095?

0 Mahesh Venugopal over 12 years ago in reply to Devin Cottier

Intellectual 415 points

Hi Devin

I dont know how to get in those scale.I hav directly plotted the following address:

regards

Mahesh

0 Devin Cottier over 12 years ago in reply to Mahesh Venugopal

TI__Guru 60865 points

The result registers you are looking at there are left aligned, so 48 is 0x0030 = 3 LSBs above 0V. This is within reason for what might be expected when sampling ground.

0 Mahesh Venugopal over 12 years ago in reply to Devin Cottier

Intellectual 415 points

Hi Devin

How can i make it to proper values(other than left aligned)?

Also how to obtain the graph for that?

regards

Mahesh

0 Devin Cottier over 12 years ago in reply to Mahesh Venugopal

TI__Guru 60865 points

The best way to get right aligned values are to use the AdcMirror registers, which are the same as the result registers, just right aligned. You can also use a right shift on the result registers: ADCRESULT0 >> 4

As far as graphing, I am not sure exactly, but I think you will want to run some code to perform sampling which moves each sample to an array in memory, then graph that array.

0 Igor Gorbachev over 12 years ago

Guru 20525 points

Hello Mahesh!

You read: "the graph when ADC pins are grounded".

1 Your digital ground and analog ground are separated or aggregated? The result would be better if they are separated.

2 On my opinion "3 LSB" is too much for the ADC-noise. It should be no more "2 LSB".

3 I think it will be helpful for you http://e2e.ti.com/support/microcontrollers/c2000/f/171/p/264395/932865.aspx#932865.

Regards,

Igor

0 Gautam Iyer over 12 years ago in reply to Mahesh Venugopal

Guru 192875 points

Hi Mahesh,

To be precise, please implement the following:

Voltage1 =((AdcRegs.ADCRESULT0>>4) );

and add Voltage1 to watchpoint and plot the graph for this variable.

Regards,

Gautam Iyer

C2000™︎ microcontrollers

C2000 microcontrollers forum

ADC values in graph- F28335- CCS4