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ADS1298 24 bit to 16 bit conversion

Ekrem Bayraktar
Expert 1190 points
Other Parts Discussed in Thread: ADS1298

Hi all,

There is an issue that I cannot understand completely. ADS1298 data sheet says that the output digital data is 2's complement MSB first. The sample program for EVM 5515 uses 16 bits for signal operation, hence down samples the signal to 16 bits. The code from the sample code is below:

 ECGDataSample[col] = ECGDataSample[col] >> 4;
 ECG_DataSample[col] = (short) ECGDataSample[col];

If I make the operation like above I also observe the ECG signal with my own host program, but what about the sign bit. Because when we crop the 24 bit data by throwing away the first and last 4 bits we loose the sign bit.

What am I missing, 

Thanks in advance.

  • 0
    TI__Guru**** 180991 points

    Hi Ekrem,

    I'm not familiar enough with the sample code the for the 5515 to provide you with an immediate answer here.  The code out from the ADS1298 is 2's comp, 24-b MSB first, but the 4-bit shift does not make immediate sense to me either.  Let me look through the original source and I'll see if I can help you track this down.

  • 0 in reply to Tom Hendrick
    Expert 1190 points

    Tom Hendrick said:

    Hi Ekrem,

    I'm not familiar enough with the sample code the for the 5515 to provide you with an immediate answer here.  The code out from the ADS1298 is 2's comp, 24-b MSB first, but the 4-bit shift does not make immediate sense to me either.  Let me look through the original source and I'll see if I can help you track this down.

    Hi Tom,

    I appreciate your help and waiting for your urgent response.

    Regards.