TMS320F2800157: DAC To ADC Loopback Test on TMS320F2800157

Hi Mazen,

Unfortunately, we do not have any examples for this.

Please refer to section 12.13.7 ADC-DAC Loopback Testing in TMS320F280015x Real-Time Microcontrollers Technical Reference Manual (Rev. B)

Let me know if you have further questions.

Thanks,

Susmitha

I looked at the section but this only theoretically answers the questions. I want to know what approach should I take to implement this test. For example, do I first intialize the cmpss dac and then the adc and then enable the loopback test in the corresponding register etc...

Also. I don't understand the concept very much. I noticed there are two comparators, one is high and one is low but when I configure the dac to set a digital value to be converted, why is there DACHVALS and DACVALS and when do I use either. I understand from this safety test that I want to configure the DAC and set a certan digital value in which the DAC will convert to an analog signal and by enabling the ADCLOOPBACK register bits this loopback signal will be fed into the adc. The output then of the adc is a digital value in which I will compare it with the dacval. if they are the same the test passed. 

I now don't undertsand why are there low and high dacval and why do I need the comparator. i only need the dac for the test.

Hi Mazen,

 If you want to have a loopback test on DAC, you simply have to program the DAC registers to output a voltage and convert this voltage through the ADC channels corresponding to the DAC that you are programming.  Let me know if this works for you.

In section 12.13.7 ADC-DAC Loopback Testing, you just need to enable loopback from analog subsystem. Attached is the related register. when you enable that, then the adc is going to sample the dac output of CMPSS regardless of adc channel selection.

Please use CMPx_DACL for DAC.

Thanks,

Susmitha

Hi Mazen,

Please also refer to Optional DAC Addition in below document. This might help.

 ADC Lab (ti.com)

The software is available in C2000Ware "training" folder - it's the ADC Lab. Here is the link

[C2000Ware_Install_Path]/training/device/[device_name]/analog_subsystems/lab_adc

Thanks,

Susmitha

Hi Mazen,

Yes, the code looks good, and your understanding is right.

Dac output can be outputted to A0/C15.The DAC output is sampled directly on an internal analog channel. There should be no need to configure the pinmux in this case. This information can be found from Table 6-16. Analog Pins and Internal Connections of datasheet.

 Please try this and let me know if you have further questions.

Thanks,

Susmitha

Is there anything I need to be doing to trigger the adc sampling? My code does the following:

function 1: 

1- COMPCTL.bit.COMPDACE = 1
2- COMPDACHCTL.bit.SWLOADSEL = 0;
3- COMPDACLCTL.bit.DACSOURCE = 0;
4- DACLVALS.bit.DACVAL = 0xFFF
5. AnalogSubsysRegs.CMPSSCTL.bit.CMP1LDACOUTEN = 0; 
6. AnalogSubsysRegs.CMPSSCTL.bit.CMPSSCTLEN = 1;

this is used to initialize the dac

function 2:

1- ADCDACLOOPBACK.all =  0xA5A50001;

This is to enable adcloopbacktest

I also initialize clock to the cmpss1 register using:

when I read the adc value in adca channel 0 the value of the result is 0 through register  AdcaResultRegs.ADCRESULT0. Am I missing something or is something more needs to be configured?

Hi Mazen,

Yes, ADC has to be triggered. Please use ADC_setupSOC to configure SOC and trigger.

There are examples in C2000ware on how to setup ADC SOC for Sampling.

[C2000Ware_Install_Path]/driverlib\f280015x\examples\adc

Thanks,

Susmitha

The test is now working according to the configurations we mentioned. However, the result of the adc is store in the following registers and not only in the result register of channel 0 and I do not want this because this affects other areas of the code. Is this the normal operation of the dac loopback test or can it be configured to only store the value in adcresult0

Hi Mazen,

How is the ADC SOC setup? Please setup SOC with ADC channel accordingly.

For example, if you configure SOC5, SOC6, SOC7, you get results stored in ADCRESULT5, ADCRESULT6, ADCRESULT7 respectively.

Thanks,

Susmitha

The ADC SOC is setup for only channel 0 and it writes in all results. Is this the normal? does the dac write the output to all result registers of the module being tested or does it output the result on channel 0 result only

Hi Mazen,

Can you send me how your ADC SOC setup configuration looks like?

Which SOC did you use?

Thanks,

Susmitha

SOC Priority = 0x0A in ADCSOCPRICTL Register
Channel Select of SOC is 0 in ADCSOC9CTL Register
TrigSeL bits are 0x03 which is cputimer2

ACQPS is 0x11 + 0x12

Hi Mazen,

I see you are using SOC9 .... Can you change to SOC0 if possible and see if issue is still happening?

Thanks,

Susmitha

I tried SOC 0 but all registers are still being written to of the ADCRESULTS Registers

Hi Mazen,

Can you try configuring to disable ADCBURSTCTL Register? This will stop multiple SOCs to run.

Meanwhile I will check with other experts, if it is common to see such.

Thanks,

Susmitha

The problem has not yet been resolved. Just to clarify, the DAC to ADC Loopback test has been working but I want to solve the problem of when the DAC outputs adc signal teh ADC then samples this signal and outputs the result to several Result Registers and this conflicts with the implementation I am tryng to do I only want the ADC to output this on just one adc result register which is ADCRESULTREGISTER0 as the SOC used is SOC0 

Hi Mazen,

On checking with experts, result should only appear in the corresponding register and not in all result registers.

You can send me the entire project here; I will try to replicate it on my end.

Thanks,

Susmitha

The following are screenshots from the register configurations:

and the following is a screenshot from the result registers when doing the dac test:

Hi Mazen,

What is other SOC configured to?

Above register info will not help me to replicate the issue. It would be great to have entire project files to reproduce here on my end.

Thanks,

Susmitha

Hello Susmitha,

I am working with Mazen and I also have the same issue.

We can't share the entire project as it's confidential with respect to our customer.

But I can share more info with you regarding the configuration of the ADC.

• We are using External VREF and configured it using AnalogSubsysRegs.ANAREFCTL.bit.ANAREFSEL = 1
• We are using both ADCA and ADC but we only perform the DAC loopback test on ADCA and ADCC isn't affected by the test.
• In ADCA we are using SOC0 to SOC8.
• Our acquisition window for all SOCs is 35
• ADC Clock is 50MHZ, we are using a pre-scaler /2.
• SYS Clock is 100MHZ.
• Al the SOCs trigger sources are timer based.
• We are using TIMER0 at 20us, TIMER1 at 100us and TIMER2 at 1ms.
• No interrupts are used for the ADC the result registers are read in the corresponding TIMER.

For SOCs to Channel mapping we have the following 

1. SOC0 -> CH4 -> Triggered by TIMER0
2. SOC1 -> CH9 -> Triggered by TIMER0
3. SOC2 -> CH10 -> Triggered by TIMER0
4. SOC3 -> CH16 -> Triggered by TIMER1
5. SOC4 -> CH3 -> Triggered by TIMER1
6. SOC5 -> CH17 -> Triggered by TIMER2
7. SOC6 -> CH1 -> Triggered by TIMER2
8. SOC7 -> CH11 -> Triggered by TIMER2
9. SOC8 -> CH12 -> Triggered by TIMER2

For the DAC configuration as Mazen mentioned before we have the following configuration

• Channel Select of DAC SOC9 is CH0 in ADCSOC9CTL Register
• Trigger is TIMER2(1ms)
• ACQPS is the same as the rest of the SOCs

I think these configurations is more than enough describing all the details needed to reproduce the issue.

Kindly note that the ADC configurations has been tested and working in our project for an entire year now, and this DAC to ADC test is crucial and blocking our development.

Hello,

While the ADC/DAC loopback mode is enabled, any SOC that is triggered will sample the DAC. If you trigger SOC5, it will sample the DAC and store the result in the ADCxRESULT5 register, regardless of what channel SOC5 is configured for. If you trigger SOC7, it will sample the DAC and store the result in the ADCxRESULT7 register, regardless of what channel SOC7 is configured for. To avoid getting results in multiple result registers, make sure to disable triggers to all SOCs except the one you wish to use for the loopback test. The triggers can then be re-enabled after the loopback mode has been turned off.

Best regards,
Ibukun

Thank you for your response this helped. 

Just another question, the Safety Manual doesn't specify whether or not the DAC to ADC loopback test should be ran in startup or also in runtime.

So is it enough to run the test in startup? will this satisfy the safety mechanism? 

Hi Hanna,

DAC to ADC loopback test can be run in either startup or in runtime. It will work either way.

Please let me know if you have any further questions. If not, please go ahead and close the thread.

Thanks,

Susmitha

Hi Susmitha,

I know that it can be run in either startup or runtime but my question is will running it only in the startup fulfill that the safety mechanism is implemented? 

Hi Hanna,

You'd normally do this at startup only. 

Thanks,

Susmitha

Running DAC to ADC Loopback test at startup only does satisfy the safety mechanism.