Simultaneous data protocol was used by Philips back in the days of the TDA1540 as the only mode it could be operated in. The TDA1541 then 1541A came later when the I²S protocol was standardized. Thus the TDA1541/A are I²S compatible. But since they were made to be compatible also with previous Philips CD hardware originally intended/designed to work with the TDA1540, they can work in simultaneous data mode... The primary reason I moved to this mode on the 1541 was its convenience when working with up to 192kHz sampling frequencies. Simultaneous mode utilizes two separate data lines, one per channel because the TDA1540 was a single DAC where each channel necessitated its own data signal. Since in this case stereo data are not multiplexed in one line as with I²S but run simultaneously, the frequencies for both master clock and bit clock can be twice as low at any given sampling frequency. Once I ran this chip in simultaneous mode and took regular audio performance measurements, I was very surprised to see its jitter performance better than I’ve ever seen it before.