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Demonstration Kit for CMX866 Reference Design



  • CMX866-based Socket Modem Reference Design
  • Fully Isolated 2-Wire Line Interface
  • Opto Isolated Ring Detect Circuitry and OptoMOS Hook Relay
  • Integral AT Command Set with 'Fast Connect'
  • PC Controlled via Terminal Emulator
  • Suits FCC68 or CTR21 DAA
  • Single 3V or 5V DC Power Supply
  • Break-Off Sections Support 'Desktop' and 'Socket' Modem Use
  • PCB Layout Data Provided


  • CMX866 Experimentation and Evaluation
  • CMX866 Reference Design

Supply Requirement:

  • 3Vdc or 5Vdc regulated power supply

The DE8661 Demonstration Board is a reference design for the CMX866 V.22 bis AT command modem IC.

The main "socket modem" section contains the CMX866 and associated components in addition to the line interface components.

Attached to the main section are two break-off sections which contain a 9-pin D type socket for PC serial communications, RJ11 line connector, supply voltage connector and a hook-state LED.

The CMX866 contains an on-chip µController, which interprets AT Commands issued via a standard terminal emulator program running on a host PC or via an external µController.

Interfacing to the Demonstration Board can be via socket pins on the socket modem section, or via the connectors provided on the break-off sections. The board can be operated at 3V or 5V dc, which must be provided by an external, regulated power supply.

The PCB has been laid out for both CTR21 and FCC68 compliant DAA designs. However the components fitted are for the simplified FCC68 design.
Instructions are given for users who wish to fit the CTR21 components.

PCB Image

DE8661: a reference design for the CMX866 V.22 bis AT command modem IC

Design Support Information


DE8661 FAQ

Q. What component modification do I have to make to my DE8661 Board to make it CTR21 compliant?

Q. I want to improve/increase the return loss of my DE8661 board, How should I do this?

A. The DE8661 uses the same line interface as the DE8681 and is described in the same Application Note. To make this board CTR21 compliant and to reduce the return loss, please refer to the application note: CMX867 and CMX868 V.22bis and V.22 modem design guide (DAA reference design).

Please note the CML disclaimer notice for applications and FAQ information.

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