LM4550B National Semiconductor Corporation, LM4550B Datasheet - Page 29

• Manufacturer Part Number: LM4550B
• 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

Multiple Codecs
CODEC CHAINING
Using National Semiconductor’s unique feature for chaining
together codecs, a multiple codec system can be built using
fewer interface pins. This Chain feature allows two, three or
four codecs to share a single signal input pin at the control-
ler. By setting the two LSBs of the Chain-In Control register
(74h) to a value other than the Codec Identity, a controller
can instruct a codec to disconnect its own SDATA_IN signal
and discard its own Input Frame and instead switch the
signal connected to the CIN pin through to the SDATA_IN
output pin allowing passage of an SDATA_IN signal carrying
(Continued)
FIGURE 9. Multiple Codecs using Extended AC Link
29
the Input Frame from a codec further down the chain. The
Chain-In Control register (74h) is updated at the rising edge
of SYNC therefore an instruction to enable or disable the
Chain feature takes effect in the next frame.
When the Chain feature is used the CIN pin should always
be driven. Connect CIN to either the SDATA_IN pin from
another codec or else ground CIN to prevent the possibility
of floating the SDATA_IN signal at the controller.
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