CS43L36 datasheet(38/89 Pages) CIRRUS

38 / 89 page

DS1081F3

CS43L36

4.5 Audio Serial Port (ASP)

As Fig. 4-20 shows, the null-sample bit (NSB) flag may be any bit of the least-significant sample byte. NSB-encoded

streams are assumed to contain 8 bits of nonaudio data as the LSB.

Figure 4-20. NSB Null Encoding

To send isochronous audio data to a serial port, the data pattern must be such that the LRCK/FSYNC transition preceding

any given nonnull sample on the 48-kHz serial port does not deviate by more than one sample period from a virtual clock

running at the desired sample rate. Use the following example to determine the data word as it appears on the serial port.

error = 0

for each LRCK

if(error < 1/FLRCK)

output = <<next sample>>

error = error + (1/Fs - 1/FLRCK)

else

output = NULL

error = error - 1/FLRCK

The null-sample sequences in Table 4-8 result from the example above for common sample rates. This method ensures

that the internal receive data FIFO does not underrun or overrun, which would cause audio data loss. Depending on the

internal audio data FIFOs’ startup conditions and on the serial-port clock-phase relationships, isochronous data sent from

a serial port may not adhere to the data patterns in Table 4-8. In all cases, the transmitted audio data rate matches the

stream sample rate.

4.5.5

50/50 Mode

Regardless of the state of ASP_LRCK/FSYNC, in 50/50 Mode (ASP_5050 = 1, see p. 66), the ASP can start a frame.

The ASP_STP setting (see p. 66) determines which LRCK/FSYNC phase starts a frame in 50/50 Mode, as follows:

Table 4-8. Isochronous Input Data Pattern Examples

Sample Rate (kHz)

Isochronous Data Pattern for LRCK = 48 kHz

8.000

1S5N (repeat)

11.025

[[[1s3nx2]1s4n]x5 1s3n1s4n]x4 [[1s3nx2]1s4n]x4 1s3n1s4n [[[1s3nx2]1s4n]x5 1s3n1s4n]x3

[[1s3nx2]1s4n]x4 1s3n1s4n (repeat)

12.000

1S3N (repeat)

16.000

1S2N (repeat)

22.05

[[1s1nx6]1n [1s1nx6]1n [1s1nx5]1n]x8 [1s1nx6]1n [1s1nx5]1n (repeat)

24.000

1S1N (repeat)

32.000

2S1N (repeat)

44.100

[12s1n[11s1n]x2]x3 11s1n (repeat)

48.000

1S (repeat)

Note: N = Null sample, S = Normal sample

ISO null sample indicator bit (selectable, Non‐PCM)

1: Normal sample

0: Null sample

Other bits are ignored

Audio Sample

N + 8

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