ADS131M08: ADS131M08 OCAL

Saad Jabir

Prodigy 230 points

Part Number: ADS131M08

Tool/software:

Hello,

We are developing our system with ads131m08 converters. 4 converters connected on the same api bus with different cs.

We found that the 24bits is actually much more than what we need ; 16 bits would be enough.

We can shift the conversion to divide by 256.

The question is how to deal with OCAL and GCAL registers ?

Are the subtraction/ amplification done with 24bits always even if we use only the LSB which is 16 bits?

thank you

Jabir

over 1 year ago

0 Bryan Lizon86 over 1 year ago

TI__Guru 56551 points

Hi Saad Jabir,

Our support is limited during the holiday here in the US, please expect a response most likely later this week, but early next week at the latest

-Bryan

0 Saad Jabir over 1 year ago in reply to Bryan Lizon86

Prodigy 230 points

Hi Bryne ,

Ok thank you !. Actually we divide now the 24bits number by 256 and write the twos complement into LSB of Ocal.

But it does not work .. It has no effect on the newly read values !!!!!!!!!!.

This is valid whether in continuous or gc mode.

will be waiting for your help

Wish you happy holidays !

0 Dale Li over 1 year ago in reply to Saad Jabir

TI__Mastermind 47905 points

Hi Saad,

Thank you for your patience. Yes, the calibration on this ADC operates with 24-bit format. You can do the calibration with 24-bit format, but you can get rid of the last 8-bit of the conversion data and just use high 16-bit data after your microcontroller receives the whole 24-bit conversion data.

BR,

Dale

0 Saad Jabir over 1 year ago in reply to Dale Li

Prodigy 230 points

Hi Dale ,

Does this mean that , setting the converter to 16 bit will not have effect on the calibration data. i.e. we read 16 bits and write into OCAL by strapping the upper 8 bits??

OR we need to write the OCAL before switching to 16bit??

Also , if we set the converter to 16 bits , will COMMANDS sending and receiving forms be effected?

Thank you !

Saad

0 Dale Li over 1 year ago in reply to Saad Jabir

TI__Mastermind 47905 points

Hi Saad,

You can actually do the offset calibration in 24-bit mode and then switch to 16-bit mode, or you can switch to the 16-bit mode first, then do the offset error calibration. Notice that the offset error in the 16-bit mode probably only have few codes, so the value or the number you write to the calibration register in 16-bit mode is usually small.

When you send a command to the ADC or read the data from the ADC in 16-bit mode, the word size should be 16-bit. The following timing is an example to write CH0_OCAL_LSB Register with 0xFC in 16-bit mode: