CS4218 Datasheet, PDF (14/44 Pages) Cirrus Logic – 16-Bit Stereo Audio Codec

CS4218
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.
Bits Per Frame
Minimum SCLK
Frequency
For All Modes Except SM3 Multiplier Sub Mode
32
CLKIN / 96
64
CLKIN / 48
128
CLKIN / 24
256
CLKIN / 12
SM3 Multiplier Sub Mode
64
(16 * CLKIN) / 48
128
(16 * CLKIN) / 24
256
(16 * CLKIN) / 12
Table 1. Soft Power Down Conditions
(Slave Modes only)
14
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
I²S^TM 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
DS135F1