lm4550 National Semiconductor Corporation, lm4550 Datasheet - Page 23

• Manufacturer Part Number: lm4550
• Description: Ac ?97 Rev 2.1 Multi-channel Audio Codec With Stereo Headphone Amplifier, Sample Rate Conversion And National 3d Sound
• Manufacturer: National Semiconductor Corporation

Secondary Codec Register Access Definitions
Reg 28h & Multiple Codec Option:
The AMAP bit, D9 in the Extended Audio ID Register (registers 28h), indicates whether or not the audio Codec supports Optional
AC’97 2.1 compliant AC-link slot to audio DAC mappings. AMAP = 1 in D9 indicates that the default (following cold or warm reset)
Codec slot to DAC mappings (configured via hardwirings, strap pin(s), or other methods) comform to the table below.
CHAIN_IN
Using National Semiconductor’s unique feature for chaining together codecs, a multiple codec system can be built. This chain
feature requires only a single stream back to the controller. By setting the two LSBs of register 74h to something other than the
codec ID, the codec stops sending its own SDATA_IN signal and instead passes the signal connected here out the SDATA_IN
pin. When the CHAIN_IN feature is used, another codec’s SDATA_IN pin should be connected here, or else this pin should be
grounded to prevent the possibility of floating the SDATA_IN signal at the controller. Reg 74h is updated at the rising edge of
SYNC.
Codec Mode
Primary
Secondary 1
Secondary 2
Secondary 3
Reg
28h
Extended
Audio ID
Name
Pin 46 (ID1)
NC/DV
NC/DV
GND
GND
D15 D14 D13
ID1
DD
DD
ID0
x
Pin 45 (ID0)
NC/DV
GND
NC/DV
GND
D12
x
DD
DD
D11 D10
x
x AMAP
Reg 28h ID1
D9
0
0
1
1
23
D8
D7
Reg 28h ID0
D6
(Continued)
0
1
0
1
D5
x
D4
x
PCM Left DAC
uses data from
slot #
D3
3
3
7
6
D2
x
D1
PCM Right DAC
uses data from
slot #
VRA xxxxh
D0 Default
www.national.com
4
4
8
9