Intel Pentium 4 User Manual

I/O Controller Hub 2
R
144 Intel
®
Pentium
®
4 Processor / Intel
®
850 Chipset Family Platform Design Guide
The ICH2 has weak pull-downs/pull-ups that are only enabled when the AC-Link Shut Off bit in
the ICH2 is set. This will keep the link from floating when the AC-link is off, or there are no
codecs present.
If the Shut-off bit is not set, it implies that there is a codec on the link. Therefore, the codec and
ICH2 will drive BITCLK and AC_SDOUT, respectively. However, AC_SDIN0 and AC_SDIN1
may not be driven. If the link is enabled, the assumption can be made that there is at least one
codec. If there is one or no CODEC onboard, then the unused AC_SDINx pin(s) should have a
weak (10 kΩ) pull-down to keep it from floating.
Table 33. Intel
®
AC’97 SDIN Pull-down Resistors
System Solution Pull-up Requirements
On-board Codec Only Pull-down the SDIN pin that is NOT connected to the codec
AMR Only Pull-down BOTH SDIN pins
BOTH AMR and On-board Codec Pull-down any SDIN pin that could be NC*
NOTE: If the on-board codec can be disabled, both SDIN pins must have pull-downs. If the on-board codec
can not be disabled, only the SDIN not connected to the on-board codec requires a pull-down.
9.3.1 AC’97 Audio Codec Detect Circuit and Configuration
Options
The following provides general circuits to implement a number of different codec configurations.
Refer to Intel’s White Paper Recommendations for ICHx/AC’97 Audio (Motherboard and
Communication and Network Riser) for Intel’s recommended codec configurations.
To support more than two channels of audio output, the ICH2 allows for a configuration where
two audio codecs work concurrently to provide surround capabilities. To maintain data-on-demand
capabilities, the ICH2 AC’97 controller, when configured for 4 or 6 channels, will wait for all the
appropriate slot request bits to be set before sending data in the SDATA_OUT slots. This allows
for simple FIFO synchronization of the attached codecs. It is assumed that both codecs will be
programmed to the same sample rate, and that the codecs have identical (or at least compatible)
FIFO depth requirements. It is recommended that the codecs be provided by the same vendor,
upon the certification of their interoperability in an audio channel configuration.
The following circuits (Figure 100 through Figure 103) show the adaptability of a system with the
modification of R
A
and R
B
combined with some basic glue logic to support multiple codec
configurations. This also provides a mechanism to make sure that only two codecs are enabled in a
given configuration and allows the configuration of the link to be determined by the BIOS so that
the correct PnP IDs can be loaded.

Intel Pentium 4 Specifications

General

Brand	Intel
Model	Pentium 4
Category	Computer Hardware
Language	English