ADS7128: am i reading the correct register?

Hi James,

Have a read over section 8.3.6 with regards to the RECENT_CHx registers.  From there, start with a simple manual conversion - refer to section 8.4.2 and figures 30 and 31.

thanks Tom, the problem is, i'm having a hard time just telling whether the ADS7128 is even reacting to the commands I think im giving it. Here is lengthy discussion im having with Manoj: https://e2e.ti.com/support/microcontrollers/c2000-microcontrollers-group/c2000/f/c2000-microcontrollers-forum/1217294/tms320f280039c-q1-need-help-transmitting-bitstream-on-i2c-bus-to-ads7128/4598780#4598780

is there a feedback test I can use to determine whether the ads7128 is understanding what im sending? im literally just trying to convert a .5V signal in a digital level based on 3v3 vref

Tom, I followed your advice. no joy though

WRT 8.3.6, what i gather is that you're pointing me to "...only the first conversion for the selected AIN channels must be initiated by the host" 

Then, I clicked on Manual Mode and jumped to the section here:

My understanding is that I automatically satisfy steps 1 thru 3 since....

1.  (Source: p24, section 8.4) and

2. (Source: p17, section 8.3.8)

Therefore, I can jump straight to step 4: "Configure desired channel ID in MANUAL_CHID field"

Using section 8.6.13 on pages 38 and 39, I find that I am interested in setting this field as 10b (which if I did the conversation right, is 0x2 in hex)

ok cool, now on to step 5: "Host provides Conversion Start Frame on I2C Bus" This is where things get sticky for me since I cannot find anything in the doc that defines what a "conversion start frame is" Additionally, I am not alone. In short, Cynthia says I need to "write two [dummy data] frames once I've written to the MANUAL_CHID field" 

Step 6: Host provides "conversion read frame on I2C Bus." Again, not defined anywhere, but I assume this means I need to tell the device to convert some data and send it to me (i.e., a read command). For example, read from register 0xA4 (the RECENT_CH2_LSB Register)

with all that being said, this is what I've come up with, and still no joy: 

Are there any glaring mistakes or incorrect assumptions?

I've updated my code..still no luck tho :/

Hi James,

Maybe this will help.  Here is a screen capture showing the selection of CH0 for conversion:

And then here is the read sequence, with 0.5V on CH0:

The SW tool I'm using won't let me capture any less then 10 conversion results, but you can see the 0x2590, 0x2580, 0x25A0 results in the first three transactions.

thanks, but this didn't really address/answer any of the questions that I had. also, you're introducing RMS...which im not looking for. i simply want to convert a .5VDC AIN to a 12bit output with a Vref of 3v3. Maybe i ought to take another approach...is there anyone in your shop with familiarity programming these devices using TI CCS s/w?

Hi James,

I see that Manoj has reached out to you.  Let me know how that goes.