CML - Wireline Data and Telephony - CMX868A

The CMX868A is a multi-standard modem IC for use in telephone based information and telemetry systems.

Control of the device is via a simple high speed serial bus, compatible with most types of µC serial interface. The data transmitted and received by the modem is also transferred over the same serial bus. On-chip programmable Tx and Rx USARTs meeting the requirements of V.14 are provided for use with asynchronous data and allow unformatted synchronous data to be received or transmitted as 8-bit words.

A high-quality DTMF decoder with excellent immunity to falsing on voice and a standard DTMF encoder are included. Alternatively, these blocks can be used to transmit and detect user-specific, programmed single and dual-tone signals, call progress signals or modem calling and answering tones. Flexible line driver and receive hybrid circuits are integrated on chip, requiring only passive external components to build a 2 or 4-wire line interface. The device also features a hook switch relay drive output and a Ring Detector circuit which continues to function when the device is in the Powersave mode, providing an interrupt which can be used to wake up the host µController when line voltage reversal or ringing is detected.

Block Diagram


  • V.22 bis 2400/2400 bps QAM
  • V.22, Bell 212A 1200/1200 or 600/600 bps DPSK
  • V.23 1200/75, 1200/1200, 75, 1200 bps FSK
  • Bell 202 1200/150, 1200/1200, 150, 1200 bps FSK
  • Bell 103 300/300 bps FSK
  • Low Voice Falsing DTMF Decoder
  • DTMF/ Tones Transmit and Receive
  • 'Powersave' Standby Mode


  • Telephone Telemetry Systems
  • Remote Utility Meter Reading
  • Security Systems
  • Industrial Control Systems
  • Electronic Cash Terminals
  • Pay-Phones
  • Set-Top Boxes


  • CMX868AD2 - 24-pin SOIC
  • CMX868AE2 - 24-pin TSSOP
  • CMX868AP4 - 24-pin PDIP

Supply Requirement:

  • 2.7 to 5.5 V power supply