Connect general purpose ADCs to the OMAP L137

Hi Carlos,

Welcome to the TI E2E forum. I hope you will find many good answers here and in the TI.com documents and in the TI Wiki Pages (for processor issues). Be sure to search those for helpful information and to browse for the questions others may have asked on similar topics (e2e.ti.com).

Yes. There is a way to use the McBSP to bring the data from ADC.

Please refer the below thread.

http://e2e.ti.com/support/dsp/omap_applications_processors/f/42/t/30026.aspx

Hi Rajasekaran,

Thank you very much for your welcome message!  I had already checked the TI web and wiki with no success.  I’ve also checked the link you attached but that’s more about accessing AUDIO ADCs from the ARM through a CODEC.

Our case is different; we are designing a custom expansion board for the OMAP L137 with the following requirements:

• We need to connect 10 precision ADC 24 bit precision at 2Khz ( = 432Kbps)
• We have available the MsASP and one of the EMIFA

(The problem with the Audio ADCs compared with the precision ones is mainly the DC behavior so we cannot use them. )

I haven’t found the way to connect them to one of the interfaces we have available (EMIFA or MsASP)

Thank you for your help,

Carlos

Hi Carlos,

Thanks for your post.

It is absolutely possible to use the McASP to bring the data from the ADCs to the OMAPL137 but, unfortunately not with EMIFA. We need to connect the AXR1[n] pin of the C6747 DSP is connected to the SDI pin (Serial interface) on the precision ADC's and SDOx pins are serial data outputs. You shall use SDOA, B and C of the precision ADC device into three McASP channels.

Please see the ADS7863 datasheet for your reference.

http://www.ti.com/lit/sbas383 (Page no 17, timing and control of the ADS7863 serial interface SDI)

There are thread references in which C6713 McASP shall program the SAR ADC (ADS8556) as below:

http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/114237.aspx

http://e2e.ti.com/support/dsp/tms320c6000_high_performance_dsps/f/115/t/114403.aspx

Unfortunately we don't have anything readily available for the McASP of the OMAPL137 that sets up the control register of the precision ADC device. You shall look out the above e2e threads for some application note available.

Thanks & regards,

Sivaraj K

Thank you very much for your answer.  It has been really helpful. 

In the case of this post  they are connecting the McASP to the serial interface of the ADS8556 ( which has a special signal for the Frame Sync):

http://e2e.ti.com/support/dsp/tms320c6000_high_performance_dsps/f/115/t/114403.aspx

If I understood it correctly they are interconnecting the devices this way:  

DSP McASP          ADS8556 

AXR1[x]      <--    SDOA 

AXR1[y]    < --    SDOB

AXR1[z]    < --    SDOB

AXR1[w]     --->    SDI

AFSX         ---->  CS/FS

ACLKX     ---->   SCLK

If that's correct I have a couple of questions in order to select the best ADCs for our application

1. I guess not but just in case:  Could it be connected to another ADC without Frame Sync signal (for example the ADS1258) using just the CS? 
2. Is there any other ADC with the characteristics(24bits,>=2Ksps) we are looking for and Frame Sync signal?

Thank you,

Carlos

Hi Carlos,

Sorry for the delayed response.

Have you finalized your design? 

Thanks.