Thanks a lot Dave. I understand it perfectly. I have one last query regarding the processing of the samples from AD1939 via DMA in the receiver buffer of the SPORT used in my ADSP-21489 SHARC processor.
I interfaced my pre amp circuit with the DSP and ran the sample program "21489 AD1939 I2S C Sampled-Based Talkthru" available with the installation of Visual DSP++ . Furthermore, I tweaked the code a little bit with the Background Telemetry Channel code to examine the samples received from the AD1939 in real time. As per my knowledge, AD1939 produces a digital word of 24 bit resolution but the datasheet also shows that in I2S mode, each slot produces 32 bits per sample. When I observed through the BTC, I got 32 bit samples from the ADC in 2's complement form as expected but I am not sure how to interpret that. My question is, how is 24 bit quantized digital word output extended to 32 bit fixed point integer in 2's complement form to be made available in the receiver buffer?