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ADC122S051: What is the clock mode : polarity and phase ?

Part Number: ADC122S051

Tool/software:

Hello, what is a correct clock mode in terms of clock polarity and phase? The timing diagram Figure 3 looks ambiguous : DOUT data is shown stable at the rising edge of clock pulse (so this is the perfect time for sampling) yet the text says the DIN is shifted inside the chip also at the rising edge of clock.

By definition the shifting of data must happen on both lines MISO and MOSI for both Master and Slave in sync and so is the sampling of data must be synchronized for both at the same time. But Figure 3 shows the stable times for shifting and sampling different for DOUT (MISO) and for DIN (MOSI) . This makes it difficult to find the synchronous clock edge for both to sample data.

The polarity of clock looks as been high in idle ('1') but the phase would be 2nd edge for DOUT  (phase '1'), yet 1st for DIN (phase '0') ... cannot be like that
Please help.

  • Hi Vlad,

    The SCLK should idle high (CPOL = 1), and data in (DIN/MOSI) is loaded on the rising (trailing) edges of SCLK (CPHA = 1), so SPI mode 3.

    The datasheet also mentions that data out (DOUT/MISO) is shifted out on falling edges of SCLK. That makes it so that it will be stable on the next rising edge to be read in by the controller. It might be a little unclear since it is written from the device's perspective.

    I think figure 1 does a better job of illustrating the specific timings faithfully, while figure 3 is more abstracted. Regardless, the drawings are not to scale, so go by the timing specifications and description. 

    Regards,
    Joel