Front Panel connectors - Intel HD Audio to AC97 (MSI P35 A..

Horst Franke wrote:
> In news:1186839930.144232.129730@e9g2000prf.googlegroups.com
> strommsarnac.TakeThisOut@gmail.com wrote:
>
>> Use the following. Connect the case plugs to the designated pins on
>> the mainboard.
>> However, the autodetect doesn't work, but that's not a big deal for me.
>
> Sorry *, but how should autodetect work on HW connections?
> There's no logic behind and resistance detection? (cannot believe in that)
>
>> I read somewhere else the RET-R/L are really optional
> I think this is because, the RET = GROUND connection will have
> been established somewhere else.
> Horst

One method of jack detection, is on PDF page 172, in the section entitled

"7.4.2 Audio Jack Detection Circuits"
http://support.intel.com/support/processors/tools/piu/sb/cs-014921.htm

Each of the switches shown in the diagram, is a "side contact" built into
the jack.

By using to of those four resistor circuits, it is possible to sense the
state of up to eight jacks. Two of the jacks, would be the headphone and
microphone jack, on the front of the computer case. The FP_AUDIO header
has three pins, which presumably are tied to the resistor circuit.

This is an example of a jack suitable for HDaudio. Contacts 4, 5, and 6 are
an isolated switch, which does not contact the analog signals. Some part of
contacts 4, 5, and 6, could be connected to the circuit shown on PDF page 172
of the Intel standard. If you bought two of these jacks, and wired them to
your FP_AUDIO 2x5 header, then you would have an HDaudio compatible solution.
I am not aware of any computer cases that currently do that.

http://www.cui.com/pdffiles/SJ-3567AN.pdf

Most computer cases, are not equipped with a jack such as the one above. Computer
cases have no isolated switches for indicating that a plug is present in the
jack. As a result, the switch based detection mechanism won't work.

If the motherboard is HDaudio, then RET-L and RET-R should not be
connected. The wires should be left floating. If the motherboard is an older
model, with a real AC'97 CODEC, then RET-L and RET-R should be connected.

There is a secondary jack detection method, which involves actually sensing
if there is a load connected to the port. Details of the existence of such
mechanisms, is poorly done in CODEC datasheets, and so this topic is hard
to research. Presumably, the impedance sensing method must be an AC based one,
because normally the jacks are AC coupled with capacitors. And the method must
exist, because the sound drivers are capable of detecting that something has
been plugged into the front of the computer.

Paul
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