REV. A

AD1837A

–13–

Control Register 2, the serial mode can be changed to right-

justified (RJ), left-justified DSP (DSP), or left-justified (LJ).

In the RJ mode, it is necessary to set Bits 4 and 5 to define the

width of the data-word.

The DAC serial data input mode defaults to I

Bits 5, 6, and 7 in DAC Control Register 1, the mode can be

changed to RJ, DSP, LJ, Packed Mode 1, or Packed Mode 2. The

word width defaults to 24 bits but can be changed by reprogram-

ming Bits 3 and 4 in DAC Control Register 1.

Packed Modes

The AD1837A packed mode allows a DSP or other controller to

write to all DACs and read all ADCs using one input data pin

and one output data pin. Packed Mode 256 refers to the number

of BCLKs in each frame. The LRCLK is low while data from a

left channel DAC or ADC is on the data pin and high while data

from a right channel DAC or ADC is on the data pin. DAC data is

applied on the DSDATA1 pin, and ADC data is available on the

ASDATA pin. Figures 7 to 10 show the timing for the packed

mode. Packed mode is available for 48 kHz and 96 kHz.

Auxiliary (TDM) Mode

A special auxiliary mode is provided to allow three external stereo

ADCs to be interfaced to the AD1837A to provide 8-in/8-out

operation. In addition, this mode supports glueless interface to a

single SHARC

access all eight channels of analog I/O. In this special mode,

many pins are redefined; see Table IV for a list of redefined pins.

The auxiliary and the TDM interfaces are independently

configurable to operate as masters or slaves. When the auxiliary

interface is set as a master, by programming the Auxiliary Mode

bit in ADC Control Register 2, AUXLRCLK and AUXBCLK are

generated by the AD1837A. When the auxiliary interface is set

as a slave, AUXLRCLK and AUXBCLK need to be generated

by an external ADC, as shown in Figure 13.

The TDM interface can be set to operate as a master or slave by

connecting the

M/S pin to DGND or ODVDD, respectively. In

master mode, the FSTDM and BCLK signals are outputs gener-

ated by the AD1837A. In slave mode, FSTDM and BCLK are

inputs and should be generated by the SHARC. Both 48 kHz

and 96 kHz operations are available (based on a 12.288 MHz or

24.576 MHz MCLK) in this mode.

LRCLK

BCLK

SDATA

LRCLK

BCLK

SDATA

LRCLK

BCLK

SDATA

LRCLK

BCLK

SDATA

LEFT CHANNEL

RIGHT CHANNEL

LEFT CHANNEL

RIGHT CHANNEL

LEFT CHANNEL

RIGHT CHANNEL

MSB

MSB

MSB

MSB

MSB

MSB

MSB

MSB

LSB

LSB

LSB

LSB

LSB

LSB

LSB

LSB

LEFT-JUSTIFIED MODE—16 BITS TO 24 BITS PER CHANNEL

RIGHT-JUSTIFIED MODE—SELECT NUMBER OF BITS PER CHANNEL

DSP MODE—16 BITS TO 24 BITS PER CHANNEL

1/

NOTES

1. DSP MODE DOES NOT IDENTIFY CHANNEL.

2. LRCLK NORMALLY OPERATES AT

3. BCLK FREQUENCY IS NORMALLY 64

LRCLK BUT MAY BE OPERATED IN BURST MODE.

Figure 4. Stereo Serial Modes