AD1849K datasheet(21/28 Pages) AD

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AD1849K

REV. A

–21–

DCB = “0” until the echoed DCB from the Codec also is reset

to “0” (i.e., it must poll DCB until a “0” is read). This is the

first interlock of the DCB handshake.

The DCB = “0” is echoed on SDTX in the next frame after it

was received on SDRX if a sample rate has been consistently

selected AND the clock source is generated using the internal

oscillator. Otherwise DCB = “0” will be echoed on SDTX in

the frame after at least 2 ms of consistent sample rate selection

expires. If SCLK or CLKIN is used as the clock source, the user

must guarantee that the source selection and sample rate are stable

for 2 ms before D/

C is driven HI.

Note that after sending a Control Word with DCB = “0,” the

external controller must take care not to set (or glitch) DCB =

“1” until after the echoed DCB = “0” has been received from

the Codec.

Second DCB Interlock

After it sees the DCB = “0” (and has optionally verified that

the echoed Control Word is correct), and when it is ready to

continue with the DCB handshake, the external controller

should transmit the desired and valid control information, but

now with DCB set to “1.” The external controller can then

transmit arbitrary control information until the echoed DCB

from the Codec is also set to “l” (i.e., it must poll DCB until a

“l” is read). After this Control Word with DCB = “1,” all future

control information received by the Codec during Control Mode

(i.e., while D/

C is LO) will be ignored. This is the second and

final interlock of the DCB handshake.

The Codec will echo DCB = “l” in the next frame after it was

received on SDRX if a sample rate has been consistently selected

AND the clock source is generated using the internal oscillator.

Otherwise DCB = “1” will be echoed on SDTX once one sample

rate selection has been held constant for at least 2 ms. If SCLK

or CLKIN is used as the clock source, the user must guarantee

that the source selection and sample rate are stable for 2 ms

before D/

C is driven HI. The Codec will transmit the full 64-bit

Control Word with DCB = “1” and then three-state the SDTX

pin. The external controller must continue to supply SCLK to

the Codec until all 64 bits of the Control Word with DCB = “1”

have been transmitted by the Codec, plus at least one [1] more

SCLK after this 64-bit Control Word (i.e., at least 65 SCLKs).

Note that echoing the full 64-bit Control Word makes the

AD1849K match the behavior of the CS4215.

Exit Control Mode

Control mode DCB handshake is now complete. The Codec

will remain inactive until D/

C goes HI or RESET and or PDN

are asserted.

Note that if a sample rate and a clock source have been consist-

ently selected throughout the handshake, the AD1849K and the

CS4215 DCB protocols are equivalent.

Control Mode to Data Mode Transition and Autocalibration

The AD1849K will enter Data Mode when the asynchronous

C signal goes HI. The serial interface will become active

immediately and begin receiving and transmitting Data Words

in accordance with the SCLK, FSYNC, TSIN, and TSOUT

signals as shown in Figure 6. If the Codec enters Data Mode as

a master, it will generate one complete SCLK period before it

drives FSYNC HI; FSYNC will go HI with the second rising

edge of SCLK. This allows external devices driven by SCLK to

recognize a complete FSYNC LO-to-HI transition. If an

AD1849K Codec enters Data Mode as a slave, it can recognize

a TSIN LO-to-HI transition even if SCLK is simultaneously

making its first LO-to-HI transition. In fact, the AD1849K

serial interface will operate properly even if D/

C, SCLK, and

TSIN all go HI at the same time.

See Figure 10 for a flow chart representation of a typical startup

sequence, including the DCB handshake.

Transmit 194 Data Words

to Codec

Begin audio operation

Wait for Codec to transmit

back a DCB HI

Transmit a Control Word

to Codec with DCB LO

Transmit desired Control Word

to Codec with DCB HI

Wait for Codec to transmit

back a DCB LO

Apply power while

RESET is pulled LO

and wait 50 milliseconds

Provide TSIN and SCLK

signals to Codec. Drive

RESET

HI (inactive) while D/

C is LO

Bring D/

C HI

ENTER CONTROL MODE

FIRST DCB INTERLOCK

0 – 2ms

SECOND DCB INTERLOCK

0 – 2ms

EXIT CONTROL MODE

AUTOCALIBRATION

Figure 10. Typical Startup Sequence

APPLICATIONS CIRCUITS

The AD1849K Stereo Codec has been designed to require a

minimum of external circuitry. The recommended circuits are

shown in Figures 11 through 20 and summarized in Figure 21.

Analog Devices estimates that the total cost of all the compo-

nents shown in these Figures, including crystals, to be less than

$5 in 10,000 piece quantities.

Industry-standard compact disc “line-levels” are 2 V rms

centered around analog ground. (For other audio equipment,

“line level” is much more loosely defined.) The AD1849K

SoundPort is a 5 V only powered device. Line level voltage swings

for the AD1849K are defined to be 1 V rms for ADC input and

0.707 V rms for DAC output. Thus, 2 V rms input analog signals

must be attenuated and either centered around the reference

voltage intermediate between 0 V and 5 V or ac-coupled. The

CMOUT pin will be at this intermediate voltage, nominally

2.25 V. It has limited drive but can be used as a voltage datum to

an op amp input. Note, however, that dc-coupled inputs are not

recommended, as they provide no performance benefits with

the AD1849K architecture. Furthermore, dc offset differences

between multiple dc-coupled inputs create the potential for

“clicks” when changing the input mux selection.

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