AMR SLOT

8/19/2000

Audio Modem Riser (AMR) Slot: AMR is an scheme promulgated by Intel in 1997 to add an expansion audio connector to the internal PC architecture. Apparently, the underlying idea is to ease the moving of digital portions of audio handling into the CPU. The analog circuitry is then placed on a plug-in card using a specialized connector known as an AC97 or AMR connector. The connector carries power, power management, control and analog phone signals. The AMR is intended only for use by manufacturers for matched AMR boards. It is not, according to Intel, intended to be used for third party cards.

AC97 is an Intel 'Audio Component' specification.

The advantages claimed for the AMR scheme include lower cost, reduced digital noise pick up, simplified certification, better quality, fewer cavities, etc,etc,etc. Some of the claims are probably legitimate

The conventional AMR implementation puts the modem telephone interface circuits, modem codec and an "isolator" (a buffer I infer) on the AMR plug in card. The motherboard generally has the audio (sound system) circuitry including the codec. The motherboard chipset routes information to the two codecs. This arrangement allows the AMR "modem" card to be certified for telephone network compliance independently from the motherboard

Since every vendor has their own version of the AC97 interface that may differ in the impedance matching of analog signals in the AMR interface, AMR cards that work with one motherboard may not work with other motherboards. Another problem is that there is no generic AMR driver and no assurance that any drivers exist that will work with an arbitrary motherboard/AMR card pair.

While some manufacturers may be using AMR as Intel intended, a number of motherboards include AMR connectors of dubious utility. A few third party AMR cards are available despite the fact that the Intel specification explicitly prohibits their use.

Full specifications for AMR can be found at

ftp://download.intel.com/ial/scalableplatforms/audio/amr101.pdf