LM4548 National Semiconductor, LM4548 Datasheet - Page 16

• Manufacturer Part Number: LM4548
• Description: AC 97 Rev 2 Codec with Sample Rate Conversion and National 3D Sound
• Manufacturer: National Semiconductor

www.national.com
Application Information
When the AC Link Codec Ready indicator bit (SDATA_IN
slot 0, bit 15) is a 1 , it indicates that the AC Link and AC ’97
registers are in a fully operational state. The AC ’97 Control-
ler must further probe the Powerdown Control / Status Reg-
ister to determine exactly which subsections are ready.
Supported powerdown modes.
Extended Audio ID Register (28h)
This read only register identifies which AC97 Extended Au-
dio features are supported. The LM4548 provides for VRA
(Variable Rate Audio) and Multiple Codec support. VRA is in-
dicated by a 1 in the LSB of register 28h. The two MSB’s,
ID1 and ID0, show the current codec configuration as con-
nected via external pins 45 and 46.
Extended Audio Status/Control Register (2Ah)
This read/write register provides status and control of the
Variable Sample Rate function. Setting the LSB of this regis-
ter to 1 enables Variable Rate Audio (VRA) mode and al-
lows DAC and ADC sample rates to be programmed via reg-
isters 2Ch and 32h.
Sample Rate Control Registers (2Ch, 32h)
These read/write registers are used to set the sample rate
for the left and right channels of the DAC (2Ch) and the ADC
(32h). When Variable Rate Audio is enabled via bit-0 of Reg-
ister 2Ah, the sample rates can be programmed, in 1Hz in-
crements, to be any value from 4kHz to 48kHz. Below is a list
of the most common sample rates and their corresponding
register values.
Pin46 (ID1)
connected)
DAC
ADC
PRO
VRA
REF
ANL
PR1
PR2
PR3
PR4
PR5
PR6
BIT
BIT
BIT
NC (not
DVdd
DVdd
GND
GND
SR15:SR0
PCM in ADC’s and Input Mux powerdown
1F40h
Analog Mixer powerdown (VREF still on)
0 = VRA off (48kHz fixed), 1 = VRA on
Digital Interface (AC Link) powerdown
Analog Mixer powerdown (VREF off)
ADC section ready to transmit data
DAC section ready to accept data
PCM out DAC’s powerdown
Pin45 (ID0)
connected)
Vref’s up to nominal level
NC (not
DVdd
DVdd
GND
GND
Analog mixers ready
Internal Clk disable
(external clk off)
Function
Function
Function
not used
Sample Rate (Hz)
8000
Reg 28h ID1
(Continued)
0
0
0
1
1
Reg 28h ID0
16
0
0
1
0
1
Reserved Registers
Do not write to these registers as they are reserved.
Codec Mode
Secondary 1
Secondary 2
Secondary 3
SR15:SR0
Primary
Primary
AC44h
BB80h
2B11h
3E80h
5622h
Sample Rate (Hz)
11025
16000
22050
44100
48000