EVAL-AD1954EB Analog Devices Inc, EVAL-AD1954EB Datasheet - Page 29

• Manufacturer Part Number: EVAL-AD1954EB
• Description: BOARD EVAL FOR AD1954
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD1954EB

• Rohs Status: RoHS non-compliant

SERIAL DATA INPUT PORT
The AD1954’s flexible serial data input port accepts data in twos
complement, MSB first format. The left channel data field always
precedes the right channel data field. The serial mode is set by
using mode select bits in the SPI control register. In all modes
except for the right-justified mode, the serial port will accept an
arbitrary number of bits up to a limit of 24 (extra bits will not
cause an error, but they will be truncated internally). In the right-
justified mode, SPI control register bits are used to set the word
length to 16 bits, 20 bits, or 24 bits. The default on power-up is
24-bit mode. Proper operation of the right-justified mode requires
exactly 64 BCLKs per audio frame.
Serial Data Input Modes
Figure 20 shows the serial input modes. For the left-justified
mode, LRCLK is high for the left channel and low for the right
channel. Data is sampled on the rising edge of BCLK. The MSB
is left-justified to an LRCLK transition, with no MSB delay. The
left-justified mode can accept any word length up to 24 bits.
In I
the right channel. Data is valid on the rising edge of BCLK. The
MSB is left-justified to an LRCLK transition but with a single
BCLK period delay. The I
number of bits up to 24.
In right-justified mode, LRCLK is high for the left channel and low
for the right channel. Data is sampled on the rising edge of BCLK.
The start of data is delayed from the LRCLK edge by 16 BCLK,
12 BCLK, or 8 BCLK intervals, depending on the selected word
length.The default word length is 24 bits; other word lengths are set
by writing to Bits 1 and 0 of Control Register 1. In right-justified
mode, it is assumed that there are 64 BCLKs per frame.
For the DSP serial port mode, LRCLK must pulse high for at
least one bit clock period before the MSB of the left channel
is valid, and LRCLK must pulse high again for at least one bit
REV. A
2
S mode, LRCLK is low for the left channel and high for
LRCLK
SDATA
LRCLK
SDATA
LRCLK
SDATA
LRCLK
SDATA
BCLK
BCLK
BCLK
BCLK
NOTES
1. DSP MODE DOESN’T IDENTIFY CHANNEL.
2. LRCLK NORMALLY OPERATES AT
3. BCLK FREQUENCY IS NORMALLY 64  LRCLK BUT MAY BE OPERATED IN BURST MODE.
MSB
2
MSB
MSB
S mode can be used to accept any
MSB
LEFT CHANNEL
LEFT CHANNEL
f
S
EXCEPT DSP MODE, WHICH IS 2 
RIGHT-JUSTIFIED MODE – SELECT NUMBER OF BITS PER CHANNEL
LEFT-JUSTIFIED MODE – 16 BITS TO 24 BITS PER CHANNEL
LSB
DSP MODE – 16 BITS TO 24 BITS PER CHANNEL
I
2
Figure 20. Serial Input Modes
S MODE – 16 BITS TO 24 BITS PER CHANNEL
LSB
LSB
–29–
LSB
clock period before the MSB of the right channel is valid. Data is
sampled on the falling edge of BCLK. The DSP serial port mode
can be used with any word length up to 24 bits. In this mode,
it is the responsibility of the DSP to ensure that the left data is
transmitted with the first LRCLK pulse and that synchronism is
maintained from that point forward.
DIGITAL CONTROL PINS
Mute
The AD1954 offers two methods of muting the analog output.
By asserting the mute signal high, the left, right, and subchan-
nels are muted. As an alternative, the user can assert the mute
bit in the serial control register high. The AD1954 has been
designed to minimize pops and clicks when muting and unmut-
ing the device by automatically ramping the gain up or down.
When the device is unmuted, the volume returns to the value
set in the volume register.
De-emphasis
The AD1954 has a built-in de-emphasis filter that can be used to
decode CDs that have been encoded with the standard redbook
50 µs/15 µs emphasis response curve. This feature may be acti-
vated by the pin or by an SPI write to the control register. When
activating with the pin, only the 44.1 kHz sample rate curve is
available. When using the SPI port, curves for 44.1 kHz, 32 kHz,
and 48 kHz are supported.
f
S
1/
.
MSB
f
S
MSB
MSB
MSB
RIGHT CHANNEL
RIGHT CHANNEL
LSB
LSB
LSB
AD1954
LSB