ADC initialization in cascade mode

abhijit choudhury

Other Parts Discussed in Thread: TMS320F28335

Hi,

My question is with ADC initialization. I am trying to use cascade mode to utilize all the 16 available pins from ADC. I check with C2000 example file for ADC, which used SEQ1 to initialize ADC A 2, 3. For my system I am using epwm 6 as a interrupt where, I am storing the ADC values and ADC is initialize in the main program. Please find my sample initialize program for ADC cascade mode attached. The program is able to access and read all 16 channels. However, my query is that I have not used any SOC from epwm 6 B to start the ADC conversion as it is done in the sample code for C2000. So is my coding is good to use?

AdcRegs.ADCTRL1.bit.CONT_RUN = 1; // This helps the sequencer to iperate in continuous mode and not in start stop mode
AdcRegs.ADCTRL1.bit.SEQ_CASC = 1; // This will set the ADC to operate in cascade 16 bit mode
AdcRegs.ADCTRL2.bit.SOC_SEQ1 = 1; // Start of convertion for cascade sequence
AdcRegs.ADCTRL3.bit.SMODE_SEL = 0; // This sets the sequential sampling mode

AdcRegs.ADCMAXCONV.all = 0x000F; // Setup maximum conversion. For 6 convertion set it as 0005.

AdcRegs.ADCCHSELSEQ1.bit.CONV00 = 0x0; // Setup ADCINA0 in cascasde mode.
AdcRegs.ADCCHSELSEQ1.bit.CONV01 = 0x1; // Setup ADCINA1 in cascasde mode.
AdcRegs.ADCCHSELSEQ1.bit.CONV02 = 0x2; // Setup ADCINA2 in cascasde mode.
AdcRegs.ADCCHSELSEQ1.bit.CONV03 = 0x3; // Setup ADCINA3 in cascasde mode.
AdcRegs.ADCCHSELSEQ2.bit.CONV04 = 0x4; // Setup ADCINA4 in cascasde mode.
AdcRegs.ADCCHSELSEQ2.bit.CONV05 = 0x5; // Setup ADCINA5 in cascasde mode.
AdcRegs.ADCCHSELSEQ2.bit.CONV06 = 0x6; // Setup ADCINA6 in cascasde mode.
AdcRegs.ADCCHSELSEQ2.bit.CONV07 = 0x7; // Setup ADCINA7 in cascasde mode.
AdcRegs.ADCCHSELSEQ3.bit.CONV08 = 0x8; // Setup ADCINB0 in cascasde mode.
AdcRegs.ADCCHSELSEQ3.bit.CONV09 = 0x9; // Setup ADCINB1 in cascasde mode.
AdcRegs.ADCCHSELSEQ3.bit.CONV10 = 0xA; // Setup ADCINB2 in cascasde mode.
AdcRegs.ADCCHSELSEQ3.bit.CONV11 = 0xB; // Setup ADCINB3 in cascasde mode.
AdcRegs.ADCCHSELSEQ4.bit.CONV12 = 0xC; // Setup ADCINB4 in cascasde mode.
AdcRegs.ADCCHSELSEQ4.bit.CONV13 = 0xD; // Setup ADCINB5 in cascasde mode.
AdcRegs.ADCCHSELSEQ4.bit.CONV14 = 0xE; // Setup ADCINB6 in cascasde mode.
AdcRegs.ADCCHSELSEQ4.bit.CONV15 = 0xF; // Setup ADCINB7 in cascasde mode.

over 5 years ago

0 Gautam Iyer over 5 years ago

Guru 192875 points

Hi Abhijit,

abhijit choudhury said:
However, my query is that I have not used any SOC from epwm 6 B to start the ADC conversion as it is done in the sample code for C2000. So is my coding is good to use?

A Good practice is to have SOC triggered by ePWM/timer module so that your sampling rate is defined. Also, you get the flexibility to further decide where exactly you want to sample during counting (up/down or both).

Regards,
Gautam

0 abhijit choudhury over 5 years ago in reply to Gautam Iyer

Prodigy 90 points

Hi Gautam,
Thank you for your reply. As, I have put the ADC sensing inside the EPWM 6, which I have already defined to execute at 6 kHz, would it not be sufficient for the ADC to take the samples at 6 kHz interrupt from their?

0 Gautam Iyer over 5 years ago in reply to abhijit choudhury

Guru 192875 points

That's fine too. You can configure as per your application requirements.

0 abhijit choudhury over 5 years ago in reply to Gautam Iyer

Prodigy 90 points

Thank you. I have another issue with the ADC sensed voltage. I have connected the ADCA0-7 and ADCB0-7 pins one by one to ground to read the ADC values inside the CCS watch window. Although most of the pins shows zero as expected, some of them is showing some digital values ranging from 16-74. Could you please suggest how can I make them zero as well. I have grounded the ADCLO pin as well. However, ADCREFM and ADCREFP pins are kept open.

0 tlee over 5 years ago in reply to abhijit choudhury

TI__Guru 62975 points

Abhijit,

Can you elaborate on your setup by letting us know which device or EVM you are using?

-Tommy

0 abhijit choudhury over 5 years ago in reply to tlee

Prodigy 90 points

Hi,

I am using TMS320F28335.

0 tlee over 5 years ago in reply to abhijit choudhury

TI__Guru 62975 points

Are you using a TI EVM or a custom board? Do you have all of the ADC input pins connected to ground simultaneously? How are you connecting to ground? Directly with something like a jumper or through a resistor?

0 abhijit choudhury over 5 years ago in reply to tlee

Prodigy 90 points

Hi,

I have eZDSP system board (Attached). I am connecting the ADC pins from P5 and P9 channels to the DSP ground pin (1 from P9eZDSP manual.pdf) ground one by one with a jumper. No resistance.

0 tlee over 5 years ago in reply to abhijit choudhury

TI__Guru 62975 points

Which signals are giving you problems? Do you have a headers installed (soldered) into the P5 and P9 ports?

What is the status of the R1 and R6 resistors?

Do you have the ADC clock divided down so as not to exceed 25MHz?

Update your code to collect a series of samples on a bad channel and share the results here. Do the same with a good channel as well.

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ADC initialization in cascade mode