CS4218 datasheet(23/44 Pages) CIRRUS

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In Master sub-mode, multifunction pins MF6:F1,

MF7:F2, and MF8:F3 select the sample fre-

quency as shown in Table 7. This table indicates

how to obtain standard audio sample frequencies

g i ve n on e of tw o CLK IN fr eq ue ncies:

12.288 MHz or 11.2896 MHz. Other CLKIN fre-

quencies may be used with the corresponding

sample frequencies being CLKIN/N. A change in

sample rate automatically initiates a calibration

cycle.

Slave Sub-Mode (SM4)

In SM4, Slave sub-mode is selected by setting

SMODE1,SMODE2 = 01. This mode configures

SSYNC and SCLK as inputs to the CS4218.

These two signals must be externally derived

from CLKIN. Since the CS4218 has no control

over the phase relationship of SSYNC and

SCLK to CLKIN, the noise performance in

Slave sub-mode may be slightly worse than

when using Master sub-mode. The CS4218 inter-

nally sets the sample frequency by sensing the

ratio of SCLK to CLKIN; therefore, for a given

CLKIN frequency, the sample frequency is se-

lected by changing the SCLK frequency. A

change in sample rate automatically initiates a

calibration cycle. Table 9 shows the sample rates

generated with two example clocks.

SM4-Slave allows up to four codecs to occupy

the same audio serial port. Table 8 lists the pin

configurations required to set the serial audio

port up for 32, 64, or 128 bits-per-frame (BPF).

Since each codec requires one sub-frame of

32 bits, 64 bits-per-frame allows up to two

codecs to occupy the same audio serial port, and

128 bits-per-frame allows up to four codecs to

occupy the same audio serial port. When set up

for more than one codec on the bus, other pins

are needed to select the particular time slot (TS)

associated with each codec. MF8:SFS2 selects

the time slot when in 64 BPF mode, and

MF8:SFS2 and MF7:SFS1 select one of four

time slots when in 128 bits-per-frame mode. Ta-

ble 8 lists the decoding for time slot selection.

Fs (kHz)

MF6:

MF7:

MF8:

with CLKIN

12.288

11.2896

MHz

256

48.00

44.10

384

32.00

29.40

512

24.00

22.05

640

19.20

17.64

768

16.00

14.70

1024

12.00

11.025

1280

9.60

8.82

1536

8.00

7.35

Table 7. SM4-Master, Fs Select

MF6:

MF7:

MF8:

Bits Per

Time

SFS1

SFS2

Frame

Slot

(BPF)

(TS)

000

001

Reserved

010

011

100

128

110

128

101

128

111

128

Table 8. SM4-Slave, Audio Port BPF & TS Select

SCLK to CLKIN Ratio

Fs (kHz)

BPF

with CLKIN with CLKIN

128

12.288 MHz 11.2896 MHz

48.00

44.10

32.00

29.40

24.00

22.05

19.20

17.64

16.00

14.70

12.00

11.025

9.60

8.82

8.00

7.35

Table 9. SM4-Slave, Fs Select.

CS4218

DS135F1

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