Programming the ADS7957

Hi Jay,

Barry never got back to us regarding his programming issues on the ADS7957 referenced in this post:

http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/49387.aspx

So I'll pose the same question to you, can you send a screen capture of your serial interface?  The most common cause of programming issues with the ADS795x family of parts is the clock to data phase relationship. 

Tom,

I will get the waveform tomorrow. What SPI mode should I be using? I think I read it is 0, is this correct?

Also, I'm trying to communicate with the part using a TMS320F28335 using McBSP-A. This peripheral works fine with a TI DAC and a Microchip EEPROM, but can you recommend a configuration for the ADS7957.

Thanks,

Jay

Hi Jay,

From the original SPI definition, you should be looking at SPI mode 1 for the ADS7957.  The SCLK dwells low and the falling edge of SCLK is the 'valid data' edge WRT the the MISO/MOSI input/output.  This would be 'clock stop with delay' I believe with the TMS320 McBSP peripheral set up to emulate an SPI interface.

Which DAC are you using?  How fast is your SCLK?

Tom,

The waveform is in the attached file.

I am using the ADS7957.

Thanks,

Jay

7802.adcWaveform.doc

Hi Jay,

Your word document is posted, but it appears to be a blank page.  I've attached a document with some screen captures from my side.  Please take a look through the document and let me know if that helps resolve your programming issues on the ADS7957.

 

Tom, I'm not sure what happened with the document, but I think my problem has been resolved. From the data sheet I was using the command described in section Continued Operation in a Selected Mode. Instead of using this I set D15-12 to 0010 and I now see the channel number incrementing for each read. Thanks.