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LMX2571: “FSK I2S mode” vs “I2S bus specification”

Tolchinsky Alexander
Intellectual 290 points
Other Parts Discussed in Thread: LMX2571

Hi

I see shift on one bit in data-line between LMX2571 “FSK I2S mode” (figure 18, p.13 in Data Sheet) and “I2S bus specification” – see picture.

If I connect I2S-port of any microcontroller and I2S-port of LMX2571, I get error in data: LSB from second-channel will be in MSB-data for LMX2571. Is this true?

Probably, CLK must run when FS is not active – on figure 18 this absent…

Thanks

  • 0
    TI__Guru* 93300 points
    Hi Alex,
    Sorry for the confusion, LMX2571's I2S port is not intended to be compatible with standard digital audio I2S specification. This is because we do not expect this port to be communicated with an audio device. The data stream in the port is not digitized audio, it is the instantaneous FSK frequency deviation as calculated from datasheet Equation 4 to 6.
    You are right, the I2S CLK must run even when FS is not active. We will update the datasheet later.
  • 0 in reply to Noel Fung
    Intellectual 290 points

    Hi Noel

    Thank You for answer.

    I2S-port has stable stream without jitter - it is good for FSK-Modulation.

    I2S-port in microcontroller can has a little FIFO and good Audio-PLL. The microcontroller can recalculate samples (not obligatory audio) in deviation. 

    Thanks,

    Alexander