CS43L36 datasheet(37/89 Pages) CIRRUS

37 / 89 page

DS1081F3

CS43L36

4.5 Audio Serial Port (ASP)

programmed such that data from a given SCLK period is assigned to more than one channel. However, an exception exists

for the DAI as the same data can be used for both received channels’ location, if desired. For an example, see Section 5.1.

Fig. 4-19 shows channel location and size. See ASP_RX0_2FS (p. 78).

Figure 4-19. Example Channel Location and Size

4.5.4

Isochronous Serial-Port Operation

In Isochronous Mode, audio data can be transferred between the internal audio data paths and a serial port at isochronous

frequencies slower than the LRCK frequency. In all cases, the sample rate/LRCK frequency ratio must be one for which

there are points at which rising edges regularly align.

Notes: Combining an isochronous audio stream on a channel (or on multiple channels) concurrently with a native audio

stream on another channel (or other multiple channels) is not supported.

In Isochronous Mode, if a stream’s sample rate does not match the LRCK frequency, it must include nulls, indicated by

the negative full-scale (NFS) code (1 followed by 0s) or by adding nonaudio bits (NSB Mode) to the data stream.

SP_RX_NFS_NSBB (see p. 77) selects between the NFS and NSB modes.In NFS Mode, to achieve a desired

isochronous output sample rate, a null-insert block adds NFS samples to the output stream. NFS samples input to the

null-insert block are incremented and are passed to the output as valid, nonnull samples.

In NSB Mode, a null-insert block adds 8 bits to the data stream and inserts null samples to achieve a desired isochronous

output sample rate. Inserted null samples are defined as NFS including the nonaudio bits. NFS samples that are input to

the null-insert block are passed as valid, nonnull samples to the output. Valid samples are indicated by a nonzero value

in the null sample indicator bit. The null sample indicator bit is globally defined by the SP_RX_NSB_POS (see p. 77). Total

data stream sample width, including the nonaudio bits, is N + 8 bits. Therefore, the maximum HD audio sample width is

24 bits in NSB Mode.

In NFS Mode, a null-remove block deletes null samples, restoring the stream’s original sample rate. NFS samples that are

input to the null-remove block are removed from the data stream as invalid, null samples.

In NSB Mode, a null-remove block deletes samples that have a zero null sample indicator bit, restoring the stream’s

original sample rate. Furthermore, the output data has the least-significant 8 bits of nonaudio data removed. Samples with

a zero null sample indicator bit are removed from the data stream as invalid, null samples.

In either NSB or NFS Mode, setting the Rx rate fields (SP_RX_FS, see p. 78) matters only if an isochronous mode is

selected via SP_RX_ISOC_MODE (see p. 77). Supported isochronous rates are 48k, 96k, and 192k. The ASPx Rx rate

bits are used only to help determine when to remove nulls and to provide the correct fSI/fSO to the SRCs while in

Isochronous Mode.

For null-remove operations, the rates do not need to match the actual data rate. Likewise, if data is being or captured at

its native rate, these registers have no effect.

Slot 0

SCLK

Slot 1

Slot 62

Slot 63

503

504

511

70 7

First SCLK latching edge of a new frame after frame sync

Traditional

‘Slot’

Ch. M MSB

Ch. M LSB

Ch. M MSB

Ch. M LSB

Ch. M MSB

Channel Resolution = 00

Channel Resolution = 01

Channel Resolution = 10

Channel Location = N

TDM

Channel M Data

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