Cirrus-logic CS4385 Manuel d'utilisateur télécharger pdf (Page 26)

26 DS671F2

CS4385

4.3.5 TDM

The TDM serial audio interface format operates in Single-, Double-, or Quad-Speed Mode and will slave

to SCLK at 256 Fs. Data is received most significant bit first on the first SCLK after an LRCK transition

and is valid on the rising edge of SCLK. LRCK identifies the start of a new frame and is equal to the sam-

ple rate, Fs. LRCK is sampled as valid on the rising SCLK edge preceding the most significant bit of the

first data sample and must be held valid for one SCLK period. Each time slot is 32 bits wide, with the valid

data sample left-justified within the time slot with the remaining bits being zero-padded.

4.4 Oversampling Modes

The CS4385 operates in one of three oversampling modes based on the input sample rate. Mode selection

is determined by the M4, M3 and M2 pins in Hardware Mode or the FM bits in Software Mode. Single-Speed

mode supports input sample rates up to 50 kHz and uses a 128x oversampling ratio. Double-Speed Mode

supports input sample rates up to 100 kHz and uses an oversampling ratio of 64x. Quad-Speed Mode sup-

ports input sample rates up to 200 kHz and uses an oversampling ratio of 32x.

The auto-speed mode detect feature allows for the automatic selection of speed mode based off of the in-

coming sample rate. This allows the CS4385 to accept a wide range of sample rates with no external inter-

vention necessary. The auto-speed mode detect feature is available in both hardware and Software Mode.

4.5 Interpolation Filter

To accommodate the increasingly complex requirements of digital audio systems, the CS4385 incorporates

selectable interpolation filters for each mode of operation. A “fast” and a “slow” roll-off filter is available in

each of Single, Double, and Quad-Speed modes. These filters have been designed to accommodate a va-

riety of musical tastes and styles. The FILT_SEL bit is used to select which filter is used (see the “Filter

Plots” on page 48 for more details).

When in Hardware Mode, only the “fast” roll-off filter is available.

Filter specifications can be found in Section 1, and filter response plots can be found in Figures 28 to 51.

DAC_B3

LRCK

SCLK

LSBMSB LSBMSB LSBMSB LSBMSB LSBMSB

SDIN1

DAC_A1 DAC_B1 DAC_A3DAC_A2

256 clks

32 clks 32 clks 32 clks 32 clks 32 clks

LSBMSB

DAC_A4

32 clks

LSBMSB

DAC_B2

32 clks

LSBMSB

DAC_B4

32 clks

LSB

LSBMSB

zero

Data

Figure 19. Format 12 - TDM Mode

1 2 ... 21 22 23 24 25 26 27 28 29 30 31 ... 54 55

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Cirrus-logic CS4385 Manuel d'utilisateur Page 26

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