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Evaluation Kit for CMX850 Communications


  • Fully Isolated 2-Wire Line Interface with FCC68 or CTR21 DAA
  • Modem Calling/Answering and CLI Firmware
  • Full Access to Unused (850) 80C51 Ports
  • 'AT' Command Compatible Firmware
  • Control via PC Terminal Emulator
  • Opto-Isolated Ring Detect Circuitry and OptoMOS Hook Relay
  • Keyboard Encoder
  • 8k byte Internal RAM
  • 4M bit External FLASH
  • 64kbyte External RAM
  • On-Board FLASH Reprogramming
  • Separate Dual Analogue-to-Digital Inputs
  • Dual Low-Power PWM Outputs
  • User's Prototyping Area
  • Provision for Optional Telco-Specific Components
  • V.22 bis, V.22, V.23, V.21 (and Bell Equivalents) Integral Modem


  • Evaluation and Investigation
    of the CMX850 IC

Supply Requirement:

  • 3.0 to 3.6 V power supply

The EV8500 EvKit comprises a single board containing a CMX850 Communications Controller (80C51 core and V.22 bis Modem IC), line interface components and a serial communications port for interfacing to a PC.

Firmware is provided to implement a standard ‘AT’ commands interface which is used to control the evaluation board via a standard terminal emulator. PC software is provided to support serial downloading of firmware updates to the evaluation kit.

The board is powered from a single 3 to 3.6 V power supply. Removal of jumpers allows the user to measure device current. Important signals can be monitored via test points and header pins.

The evaluation board has a 2-wire line interface to provide line matching and dc isolation.
This 2-wire interface is connected to the line using an OptoMOS relay.

Where components are telco-specific (line impedance, line protection, etc.) space is provided for the user to add appropriate components.

PCB Image

EV8500: evaluation kit for CMX850 Communications Controller IC

Design Support Information


EV8500/CMX850 FAQ

Q. I have been trying to write my own code to the EV8500 Flash memory but keeping getting the message: "Unable to Reset FLASH Memory for Programming". I have done everything the EV8500 manual tells me to do, such as ensuring that the thin stub is included in the new software, but it still does not work?

A. The likely scenario for this is that you are using the wrong type of FLASH memory for the EV8500 board. After changing the appropriate jumper settings and resetting the board, the thin stub is next used to set-up the serial link to the local PC ready for the thick stub to be downloaded. Once the thick stub has been installed into XRAM, one of its first tasks is to validate the FLASH memory. This is performed by reading the unique identification number that is built into the FLASH, if it does not read the code "29LV040" it will then flag an error.

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