Asus M3A76-CM - Manual (Page 36)

12. Optical drive audio in connector (4-pin CD)
This connector allows you to receive stereo audio input from sound sources such as a
CD-ROM, TV tuner, or MPEG card.
13. Chassis intrusion connector (4-1 pin CHASSIS)
This connector is for a chassis-mounted intrusion detection sensor or switch. Connect
one end of the chassis intrusion sensor or switch cable to this connector. The chassis
intrusion sensor or switch sends a high-level signal to this connector when a chassis
component is removed or replaced. The signal is then generated as a chassis intrusion
event.
By default, the pin labeled “Chassis Signal” and “Ground” are shorted with a jumper
cap. Remove the jumper caps only when you intend to use the chassis intrusion
detection feature.
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