LM4546B datasheet(17/27 Pages) NSC

17 / 27 page

AC Link Serial Interface Protocol

(Continued)

checks the valid-data bits for 4 slots. In Primary mode these

tag bits are for: slot 1 (Command Address), slot 2 (Command

Data), slot 3 (PCM data for left DAC) and slot 4 (PCM data

for right DAC).

The last two bits in the Tag contain the Codec ID used to

select the target codec to receive the frame in multiple codec

systems. When the frame is being sent to a codec in one of

the Secondary modes the controller does not use bits 14 and

13 to indicate valid Command Address and Data in slots 1

and 2. Instead, this role is performed by the Codec ID bits –

operation of the Extended AC Link assumes that the control-

ler would not access a secondary codec unless it was pro-

viding valid Command Address and/or Data. When in one of

the secondary modes the LM4546B only checks the tag bits

for the Codec ID and for valid data in the two audio data slots

3&4.

When sending an Output Frame to a Secondary mode co-

dec, a controller should set tag bits 14 and 13 to zero.

SLOT 0, OUTPUT FRAME

Bit

Description

Comment

Valid Frame

1 = Valid data in at least one

slot.

Control register

address

1 = Valid Control Address in

Slot 1 (Primary codec

only)

Control register

data

1 = Valid Control Data in Slot

2 (Primary codec only)

Left DAC data

in Slot 3

1 = Valid PCM Data in Slot 3

(Primary & all Secondary

modes)

Right DAC data

in Slot 4

1 = Valid PCM Data in Slot 4

(Primary & all Secondary

modes)

10:2

Not Used

Controller should stuff these

slots with “0”s

Bit

Description

Comment

1,0

Codec ID

(ID1, ID0)

The codec ID is used in a

multi-codec system to identify

the target Secondary codec for

the Control Register address

and/or data sent in the Output

Frame

SDATA_OUT: Slot 1 – Read/Write, Control Address

Slot 1 is used by a controller to indicate both the address of

a target register in the LM4546B and whether the access

operation is a register read or register write. The MSB of slot

1 (bit 19) is set to 1 to indicate that the current access

operation is ’read’. Bits 18 through 12 are used to specify the

7-bit register address of the read or write operation. The

least significant twelve bits are reserved and should be

stuffed with zeros by the AC ’97 controller.

SLOT 1, OUTPUT FRAME

Bits

Description

Comment

Read/Write

1 = Read

0 = Write

18:12

Address

Identifies the Status/Command

11:0

Reserved

Controller should set to "0"

SDATA_OUT: Slot 2 – Control Data

Slot 2 is used to transmit 16-bit control data to the LM4546B

when the access operation is ’write’. The least significant

four bits should be stuffed with zeros by the AC ’97 controller.

If the access operation is a register read, the entire slot, bits

19 through 0 should be stuffed with zeros.

SLOT 2, OUTPUT FRAME

Bits

Description

Comment

19:4

Control

Data

Controller should stuff with

zeros if operation is “read”

3:0

Reserved

Set to "0"

SDATA_OUT: Slots3&4 – PCM Playback Left/Right

Channels

Slots 3 and 4 are 20-bit fields used to transmit PCM data to

the left and right channels of the stereo DAC for all codec

Primary and Secondary modes. Any unused bits should be

stuffed with zeros. The LM4546B DACs have 18-bit resolu-

tion and will therefore use the 18 MSBs of the 20-bit PCM

data (MSB justified).

SLOTS3&4, OUTPUT FRAME

Bits

Description

Comment

19:0

PCM DAC Data

(Left /Right

Channels)

Slots used to stream data to

DACs for all Primary or

Secondary modes.

Set unused bits to "0"

20123305

FIGURE 5. Start of AC Link Output Frame

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