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AMR Modem Riser

AMR (Audio/Modem Riser) cards were used towards the end of the "modem days" where the actual analog modem was completley implemented in software, interconnected via a kind of sound card to a telephone jack.

In certain generations of PCs, the mainboard contained an AC-Link interface to which external codec ICs (ADC/DAC) are attached. To avoid mainboards having to include the [expensive, space-consuming] line interface circuitry on-board, the AMR connector was defined by Intel. This way the AC97 modem codec IC and analog line interface was pushed to an extension card.

See the AMR specification attached in amr.pdf for details on the AMR form-factor, as well as ac97_r23.pdf for the AC97 specification covering the AC-Link interface.

AMR mechanical connector

The mechanical connector is a TE connectivity 5650090-7‎ PCB edge connector:

AZTECH MR2800-W

This is an example of an AC97 codec based modem implemented in the AMR form-factor.

The original user manual can be found in aztech_mr2800w_amr_modem.pdf

In 2021, it is available for purchase as a low-cost surplus part from Pollin at https://www.pollin.de/p/amr-modem-aztech-mr2800-w-platine-mit-2a-relais-2-wechsler-700509

Si3014 + HAMR5603 DAA chipset

As can be seen on the picture, it consists of a combination of Si3014 and HAMR5603. The data sheet for the Si3014 is available, but for the HAMR5603 we couldn't find it so far.

It seems like originally the Si3014 was supposed to be paired with a Si3024 (the combination being called Si3038), see si3038_si3014_si3024_softmodem_ac97.pdf

AMBIT T60M283

This is a laptop version of an AC97 modem, obviously with a different physical form-factor

Talking to AMR modems in 2021

There is some work ongoing to create a break-out board (#5294) and an iCE40 based AC97-to-USB adapter, with the idea being to use those AMR cards as low-cost analog phone ADC/DAC interface for playing with linmodem

Updated by laforge 11 months ago · 4 revisions

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