AD1835 Analog Devices, AD1835 Datasheet - Page 18

• Manufacturer Part Number: AD1835
• Description: 2 ADC, 8DAC 96 Khz, 24-Bit Sigma Delta Codec
• Manufacturer: Analog Devices

AD1835
CONTROL/STATUS REGISTERS
The AD1835 has 15 control registers, 13 of which are used to
set the operating mode of the part. The other two registers,
ADC Peak 0 and ADC Peak 1, are read-only and should not
be programmed. Each of the registers is 10 bits wide with the
exception of the ADC peak reading registers which are 6 bits
wide. Writing to a control register requires a 16-bit data frame
to be transmitted. Bits 15 to 12 are the address bits of the
required register. Bit 11 is a read/write bit. Bit 10 is reserved
and should always be programmed to 0. Bits 9 to 0 contain the
10-bit value that is to be written to the register or, in the case of a
read operation, the 10-bit register contents. Figure 3 shows
the format of the SPI read and write operation.
DAC Control Registers
The AD1835 register map has 10 registers that are used to control
the functionality of the DAC section of the part. The function
of the bits in these registers is discussed below.
Sample Rate
These bits control the sample rate of the DACs. Based on a
24.576 MHz IMCLK, sample rates of 48 kHz, 96 kHz, and
192 kHz are available. The MCLK scaling bits in ADC
Control III should be programmed appropriately, based on the
master clock frequency.
Power-Down/Reset
This bit controls the power-down status of the DAC section.
By default normal mode is selected, but by setting this bit, the
digital section of the DAC stage can be put into a low-power
mode, thus reducing the digital current. The analog output
section of the DAC stage is not powered down.
DAC Data-Word Width
These two bits set the word width of the DAC data. Compact
Disc (CD) compatibility may require 16 bits, but many modern
digital audio formats require 24-bit sample resolution.
DAC Data Format
The AD1835 serial data interface can be configured to be
compatible with a choice of popular interface formats, including
I
are given in the Serial Data Port section of this data sheet.
De-Emphasis
The AD1835 provides built-in de-emphasis filtering for the
three standard samples rates of 32.0 kHz, 44.1 kHz, and 48 kHz.
Mute DAC
Each of the eight DACs in the AD1835 has its own independent
mute control. Setting the appropriate bit will mute the DAC
output. The AD1835 uses a clickless mute function that
attenuates the output to approximately –100 dB over a number
of cycles.
Stereo Replicate
Setting this bit copies the digital data sent to the stereo pair
DAC1 to the three other stereo DACs in the system. This
allows all four stereo DACs to be driven by one digital data
stream. Note that in this mode DAC data sent to the other
DACs is ignored.
2
S, LJ, RJ, or DSP modes. Details of these interface modes
PRELIMINARY TECHNICAL DATA
–18–
DAC Volume Control
Each DAC in the AD1835 has its own independent volume
control. The volume of each DAC can be adjusted in 1024
linear steps by programming the appropriate register. The
default value for this register is 1023, which provides no attenu-
ation, i.e., full volume.
ADC Control Registers
The AD1835 register map has five registers that are used to
control the functionality and read the status of the ADCs. The
function of the bits in each of these registers is discussed below.
ADC Peak Level
These two registers store the peak ADC result from each channel
when the ADC peak readback function is enabled. The peak
result is stored as a 6-bit number from 0 dB to –63 dB in 1 dB
steps. The value contained in the register is reset once it has
been read, allowing for continuous level adjustment as required.
Note that the ADC peak level registers use the six most sig-
nificant bits in the register to store the results.
Sample Rate
This bit controls the sample rate of the ADCs. Based on a
24.576 MHz IMCLK, sample rates of 48 kHz and 96 kHz are
available. The MCLK scaling bits in ADC Control III should be
programmed appropriately based on the master clock frequency.
ADC Power-Down
This bit controls the power-down status of the ADC section and
operates in a similar manner to the DAC power-down.
High-Pass Filter
The ADC signal path has a digital high-pass filter. Enabling this
filter will remove the effect of any dc offset in the analog input
signal from the digital output codes.
Dither
Enabling the dither function will add a small amount of random
charge to the sampling capacitors on the ADC inputs. This will
eliminate the effect of any idle tones that could occur if there
were no input signal present.
ADC Data-Word Width
These two bits set the word width of the ADC data.
ADC Data Format
The AD1835 serial data interface can be configured to be
compatible with a choice of popular interface formats, including
I
Master/Slave Auxiliary Mode
When the AD1835 is operating in the auxiliary mode, the auxil-
iary ADC control pins, AUXBCLK and AUXLRCLK, that
connect to the external ADCs, can be set to operate as a master
or slave. If the pins are set in slave mode, one of the external
ADCs should provide the LRCLK and BCLK signals.
ADC Peak Readback
Setting this bit enables ADC peak reading. See the ADC section
for more information.
2
S, LJ, RJ, or DSP modes.
REV. PrA