STAC9766 Datasheet, PDF (23/97 Pages) Integrated Device Technology – TWO-CHANNEL, 20-BIT, AC’97 2.3 CODECS WITH STEREO MICROPHONE AND MIC/JACK SENSING

STAC9766/9767
TWO-CHANNEL, 20-BIT, AC’97 2.3 CODECS WITH STEREO MICROPHONE AND MIC/JACK SENSING
PC AUDIO
CODECs configured as Secondary must power up with the BIT_CLK pin configured as an input.
Using the provided BIT_CLK signal is necessary to ensure that everything on the AC-link is synchro-
nous. BIT_CLK is the clock source (multiplied by 2 so that the internal rate is 24.576 MHz).
4.3.3. CODEC ID Strapping
Audio CODECs in the 48-pin package use pins 45 and 46 (defined as ID0# and ID1#) as strapping
(i.e. configuration) pins to configure the CODEC ID. The ID0# and ID1# strapping bits adopt inverted
polarity and default to 00 = Primary (via a weak internal pullup) when left floating. This eliminates the
need for external resistors for CODECs configured as Primary, and maintains backward compatibil-
ity with existing layouts that treat pins 45 and 46 as “no connect” or cap to ground. Pulldowns are
typically 1 KΩ - 10 KΩ and connected to Digital (not Analog) Ground.
Table 3. Recommended CODEC ID Strapping
CID1 (pin 46)
NC (weak internal pullup)
NC (weak internal pullup)
pulldown
pulldown
CID0 (pin 45)
NC (weak internal pullup)
pulldown
NC (weak internal pullup)
pulldown
Configuration
Primary ID 00
Secondary ID 01
Secondary ID 10
Secondary ID 11
4.4. Clocking for Multiple CODEC Implementations
To keep the system synchronous, all Primary and Secondary CODEC clocking must be derived from
the same clock source, so they are operating on the same time base. In addition, all AC-link protocol
timing must be based on the BIT_CLK signal, to ensure that everything on the AC-link will be syn-
chronous.
The following are potential 24.576 MHz clock options available to a Secondary CODEC:
• Using an external 24.576 MHz signal source (external oscillator or AC‘97 Digital Controller)
• Using the Primary’s XTAL_OUT
• Using the Primary’s BIT_CLK output to derive 24.576 MHz
See section 2.2.3: page14 for clock frequencies supported and configurations.
4.4.1. STAC9766/9767 as a Primary CODEC
Primary devices are required to support correctly either of the following clocking options:
• 24.576 MHz crystal attached to XTAL_IN and XTAL_OUT
• 24.576 MHz external oscillator provided to XTAL_IN
• 12.288 MHz oscillator provided to the BIT_CLK input
The Primary device may also optionally support the following clocking option:
• 14.318 MHz external oscillator provided to XTAL_IN
See section 2.2.3: page14 for clock frequencies supported and configurations.
IDT™
23
TWO-CHANNEL, 20-BIT, AC’97 2.3 CODECS WITH STEREO MICROPHONE AND MIC/JACK SENSING
STAC9766/9767
V 7.4 12/06