Cirrus Logic CS4385 - Manual (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
LSB MSB LSB MSB LSB MSB LSB MSB LSB MSB SDIN1
DAC_A1 DAC_B1 DAC_A3 DAC_A2
256 clks
32 clks 32 clks 32 clks 32 clks 32 clks
LSB MSB
DAC_A4
32 clks
LSB MSB
DAC_B2
32 clks
LSB MSB
DAC_B4
32 clks
LSB
LSB MSB zero
Data
Figure 19. Format 12 - TDM Mode