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CCS/PGA900: Reading ADC Code

maryem zanned
Prodigy 160 points

Other Parts Discussed in Thread: PGA900

Tool/software: Code Composer Studio

Hi TI Experts

I configured both of the AFE P and T channels of the PGA900 as mentioned in data sheet and i've been able to read from both of ADC the problem is the values written in ADC registers don't make any sense accordin to the inputs values !!! 

Is there any specific formula that theise ADC use to convert input data ? I have tried the formula mentioned in the PGA900 application  (Single-Chip, Loop-Powered 4- to 20-mA RTD Sensor Transmitter ) but still the values have no relation with the input ! 

same thing for the DAC !

can you save me please !

Regards 

  • 0
    TI__Mastermind 31655 points
    Hi Maryem,

    Are you attempting to read the ADC values in real time using the digital interface (SPI/I2C/OWI)? The problem with this method is that you have to read a large amount of data from registers that are constantly being updated by as the ADC outputs new values. For example, by the time you read PADC_DATA1, the ADC may have output new data, so when you start to read PADC_DATA2 it does not fit with the previous data from PADC_DATA1.

    In order to properly output the ADC data in a digital format, you will have to run the M0 microcontroller, and use the communication buffer. In your M0 code, you will have the M0 store the values from the ADC as soon as they are updated. Then they can be passed through the COMBUF register to be accessed by the digital interfaces. Please see section 7.3.13.1 of the datasheet "Accessing PGA900 Memories While Microprocessor is Running".

    The PGA900 reference firmware includes a COMBUF file with shell functions for the COMBUF transactions. It can be downloaded from the tools and software page here: www.ti.com/.../toolssoftware

    Regards,
  • 0 in reply to Scott Cummins
    Prodigy 160 points

    Hi Scott

    Am I going to need XDS200 ?

    Regards