PDB adc trigger issue

[gnichimohamed]

Hello

I am trying to trigger two adc channels from pdb on the K02.

Here us my code so far

SIM->SCGC6|=SIM_SCGC6_PDB(1);// enable clock for pdb
PDB0->SC|=PDB_SC_TRGSEL(0xF)     |//soft trigger
                      PDB_SC_PRESCALER(1) |
                      PDB_SC_MULT(0) |
                      PDB_SC_CONT_MASK |PDB_SC_PDBIE_MASK|
                      PDB_SC_PDBEN(1);

PDB0->CH[0].C1|=PDB_C1_BB(0x02) |PDB_C1_EN(0x03);
PDB0->MOD=2000;
PDB0->IDLY=2000;
PDB0->SC |= PDB_SC_LDOK_MASK;
SIM->SCGC6 |= SIM_SCGC6_ADC0_MASK; //enable clock for ADC0
ADC0->SC2 |=ADC_SC2_ADTRG_MASK;
ADC0->SC1[0]=ADC_SC1_ADCH(0x11);//ADC0CH11
ADC0->SC1[1]=ADC_SC1_ADCH(0x5);//ADC0CH5
ADC0->SC1[1]|=ADC_SC1_AIEN_MASK;
ADC0->CFG1 |=ADC_CFG1_MODE(0x03);

EnableIRQ(ADC0_IRQn);
NVIC_SetPriority(ADC0_IRQn, 0);
EnableIRQ(PDB0_IRQn);
NVIC_SetPriority(PDB0_IRQn, 1);
PDB0->SC |=PDB_SC_SWTRIG_MASK|PDB_SC_LDOK_MASK;

The problem is i can get the pdb interrupt to occur but the ADC interrupt seems to happen only ones at the start.
Thanks for the help.

[gnichimohamed]

So the issue is that i didn't activate the pre-triggers and the right delay so that the second pre-trigger will work.

PDB0->CH[0].C1|=PDB_C1_BB(0x02) |PDB_C1_TOS(0x03)|PDB_C1_EN(0x03);

Now there is two successive conversion on analog channel 5 and 11.

I wanted to check if the ADC is as accurate as it should be in this configuration so i used only channel 11 to be triggered two times in a row and look at the RA and RB results. When i use 16 bit conversion there is big differences between the two readings but in 12 bit mode the values are always exactly the same. I wonder if anyone has the same issue. Or have i done something wrong?

[Robin_Shen]

Sorry for the late reply.
Yes you are right. The ADC module need time to achieve AD conversion. So you need set enough delay between two pre-trigger.
From the K02P64M100SFA DataSheet you can find below description:

So the analog channel 5 and 11(17) only meet the 13-bit differential/12-bit single-ended accuracy specifications.

And the analog channel 11 is not available for your chip. I think it's analog channel 17.

Best Regards,

Robin

[gnichimohamed]

Thank you Robin.

I set/

ADC0->SC1[0]=ADC_SC1_ADCH(0x01);
ADC0->SC1[1]=ADC_SC1_ADCH(0x01);  //using PTE17 as ADC0_DP1

Even in 12bit mode there are big errors? I start to question my ADC config or i can't use two the same ADC0_DP1 analog channel on both ADC conversion channels?

[Robin_Shen · Accepted solution]

When you set:
ADC0->SC1[0]=ADC_SC1_ADCH(0x01);
ADC0->SC1[1]=ADC_SC1_ADCH(0x01);  //using PTE16 as ADC0_DP1
PTE16 should be the singal input pin.

If you input the singal at PTE17, then AD channel 21 should be configured as below:
ADC0->SC1[0]=ADC_SC1_ADCH(0x15);
ADC0->SC1[1]=ADC_SC1_ADCH(0x15);  //using PTE17 as ADC0_DM1

Even in 12bit mode there are big errors?

No. You can have a try after selected the correct input channel.

And I recommand this application note: AN5250 "How to Increase the Analog-to-Digital Converter Accuracy in an Application".

Best Regards,

Robin

[gnichimohamed]

Thank you Robin. I was sure there was something wrong there, i was confused with the differential config. It seems that the ADC doesn't really have the precision of a 16bit ADC. I get now small errors in readings up to 20. 

I hope that recording audio in 16bit mode will be better than 12bit. 

[Robin_Shen]

Hi Gnichi,

Have you try to use these three ADC input pins: ADC0_DP0, ADC0_DM0, ADC0_DP3. Will all these pins get 20LSB error?

16 bit is the resolution of ADC, about the precision please read the "Table 24. 16-bit ADC characteristics" in DataSheet.

And be aware of "Reference-voltage noise" and "Analog-input signal noise" in AN5250.

Best Regards,

Robin