CS4218 datasheet(14/44 Pages) CIRRUS

14 / 44 page

master and slave modes automatically initiates a

calibration.

An RC filter with a time constant greater than

50 ms may be used on the RESET pin.

The

CS4218 RESET pin has hysterisis to ensure

proper resets when using an RC filter.

Hard power down mode may be initiated by

bringing the PDN pin low. All analog outputs

will be driven to the REFBUF voltage which

will then decay to zero. All digital outputs will

be driven low and then will go to a high imped-

ance state. Minimum power consumption will

occur if CLKIN is held low. After leaving the

power down state, RESET should be held low

for 50 ms to allow the analog voltage reference

to settle before calibration is started.

Alternatively, soft power down may be initiated

in slave modes by reducing the SCLK frequency

below the minimum values shown in Table 1. In

soft power down the analog outputs are muted

and the serial data from the codec will indicate

invalid data and the appropriate error code. The

parallel bit I/O is still functional in soft power

down mode. This is, in effect, a low power mode

with only the parallel bit I/O unit functioning.

Audio Serial Interface

In Serial Mode 3 (SM3), the audio serial port

uses 4 pins: SDOUT, SDIN, SCLK and SSYNC.

SDIN carries the D/A converters’ input data and

control bits. Input data is ignored for frames not

allocated to the selected CS4218. SDOUT car-

ries the A/D converters’ output data and status

bits. SDOUT goes to a high-impedance state

during frames not allocated to the selected

CS4218. SCLK clocks data in to and out of the

CS4218. SSYNC indicates the start of a frame

and/or sub-frame. SCLK and SSYNC must be

synchronous to the master clock.

Serial Mode 4 (SM4) is similar to SM3 with the

exception of the control information. In Serial

Mode 4, the control information is entered

through a separate asynchronous control port.

Therefore, the audio serial port only contains

audio data, which reduces the number of bits on

the audio port from 64 to 32 per codec. This is

useful for lower bit rate serial hosts.

Serial Mode 5 (SM5) is compatible with the

2STM serial data protocol. SM5 is a Master

mode only. As in SM3, 4 pins are used:

SDOUT, SDIN, SCLK, and SSYNC.

The serial port protocol is based on frames con-

sisting of 1, 2, or 4 sub-frames. The frame rate is

the system sample rate. Each sub-frame is used

by one CS4218 device. Up to 4 CS4218s may be

attached to the same serial control lines. SFS1

and SFS2 are tied low or high to indicate to each

CS4218 which sub-frame is allocated for it to

use.

Serial Data Format

In SM3 and SM5, a sub-frame is 64 bits in

length and consists of two 16-bit audio values

and two 16-bit control fields. In SM4 a sub-

frame is 32 bits in length and only contains the

two 16-bit audio fields; the control data is loaded

through a separate port. The audio data is MSB

Bits Per Frame

Minimum SCLK

Frequency

For All Modes Except SM3 Multiplier Sub Mode

CLKIN / 96

CLKIN / 48

128

CLKIN / 24

256

CLKIN / 12

SM3 Multiplier Sub Mode

(16 * CLKIN) / 48

128

(16 * CLKIN) / 24

256

(16 * CLKIN) / 12

Table 1. Soft Power Down Conditions

(Slave Modes only)

CS4218

DS135F1

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