Product description

The CMX865A is a DTMF Codec/FSK Combo multi-standard modem for use in Wireless Local Loop, including Fixed Wireless Terminals and Fixed Wireless Phone installations and Short Message Service telephone systems.

Flexible line driver, hybrid and receiver circuits are integrated on chip, requiring only passive external components to build a 2 or 4-wire line interface.

POTS Signalling

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, simple melodies, call progress signals or modem calling and answering tones.

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  • V.23 1200/75, 1200/1200, 75, 1200 bps FSK
  • Bell 202 1200/150, 1200/1200, 150, 1200 bps FSK
  • V.21 or Bell 103 300/300 bps FSK
  • Low Voice Falsing DTMF Decoder
  • DTMF/Tones Transmit and Receive
  • Low Power – High Performance
  • ‘Powersave’ Standby Mode
  • Can achieve simple voice record and playback actions


  • Wireless Local Loop
  • Fixed Wireless Terminals (FCT/FWT)
  • SMS Phones
  • Security Systems
  • Remote Utility Meter Reading
  • Industrial Control Systems
  • Pay-Phones
  • Set-Top Boxes

Power supply requirement

  • 3.0 to 3.6 V power supply

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Design resources

CMX865 and CMX865A FAQ

Q. CMX865A: The DTMF de-response is given as 30ms max but I measure more than this on some DTMF digits under certain conditions.

A. The de-response time of the DTMF decoder is correct.
The programmer cannot see the DTMF response/de-response directly. What the programmer sees is b5 which loosely tracks the DTMF decoder response.

When a DTMF digit ends, the DTMF decoder will de-respond and some time later b5 will signal this by going low.
To allow for polling, the minimum time that b5 is high is 14ms. To ensure that short DTMF digits with short gaps between can be detected in the code, b5 will de-respond when energy from the following tone is detected. Under these conditions the maximum high time for b5 is 30ms. This maximum high time is called the DTMF de-response time.
Note that with longer DTMF tones and longer gaps, b5 can be high for more than 30ms.

This downloadable graphic shows the response of b5 in a number of different receive scenarios.

Q. Can you detail the differences of the CMX865A with respect to the CMX865?

A. The listings below should help you:

CMX865A Advantages over CMX865

  • Smaller package, less pins = smaller footprint
  • Pin count reduced from 24 to 16
  • V.21 function added
  • No MOQ

CMX865A Functional Difference from the CMX865

  1. The RT and RD pins are removed. The ring detector function is not required in Wireless Local Loops and most alarm systems.
    This function is easily provided by a GPI/O pin on the host micrprocessor.
    Schematics are available from CML Tech Support.
  2. The hookswitch pin is not present. This is a simple output function that is more cost-effective when moved to the host processor.
  3. The receiver interface has been simplified by making it single-ended.
    The internal hybrid function eliminates the need for a differential receiver.
  4. V.21 transceive capability has been instated for alarm panels and other niche applications
  5. 6.144MHz operation only

Development Support

  • A series of Application Notes to assist with design-ins to the target markets
  • Can be evaluated in the EV8600 Modem Evaluation Kit
  • An adapter board, HB865A, is available to allow device evaluation in a dual-in-line footprint


  • The CMX865A is designed to interface easily to a SLIC.
    All of the transmit signals are summed within the device and there is a register for software setting the output signal level (the same as the CMX865). The output can be single-ended or differential.
  • The outputs tri-state automatically when the modem is not being used thus providing a high impedance to the line. This allows simple mixing of other signals, such as voice.
  • The input is single-ended with a gain-setting, feedback path for convenience.
    Like the CMX865, the CMX865A also has a software controlled attenuator.
  • The CMX865A will provide exactly the same signalling as the CMX865 and is directly register compatible
  • The operating voltage is the same as the CMX865 but the operating current is expected to be slightly lower

CMX86x and CMX850 Filter Coefficient Generator Program

This application note comprises the Filter Coefficient Generator program as an Excel spreadsheet as well as operational instructions.

CMX8xx: Short Message Service (SMS) Implementation using CML Products

This document aims to assist modem product designers using and understanding Short Message Service (SMS) applications. CML Microcircuits' (CML) integrated circuit devices (CMX85x and CMX86x) could be used to realize and achieve a Caller Line Identification (CLI), SMS or Low Rate Messaging Service (LRMS) data transfer within a wireline system.

CLI with the CMX860, CMX865/A, CMX867/A and CMX868/A

Caller Line ID (CLI) was originally developed for the US market but has become commonplace throughout the World because of its multitudinous applications. There are a number of CLI protocols to which telephone equipment manufacturers must comply. This document gives an overview of two types; BELL GR-30-CORE/SR-TSV-002476 (or ETSI 300 659-1 section 6.1.1) used in the USA and most of the world and Caller Line Identification Presentation (CLIP) BT SIN 227 (or ETSI ETS 300 659-1 section 6.1.2c) used in the UK.

Recommendations for V.23 1200/75 b/s duplex call set-up

V.23 recommendations do not describe how a connection is established; a procedure is described below and illustrated in Figure 1; however you should not rely on other modems following this particular flow. Note also that 1200/1200 bps half-duplex connections are not covered by this application note.

CMX865A: Addressing SIA Protocols with the CMX865A

Security alarm panels are used around the world as a cost-effective means of protecting people and property. The Security Industry Association (SIA)1, a trade organization that represents security market companies, has developed protocols that describe the communications link used by these panels. DTMF tones, pulsed tones, and frequency-shift keying (FSK) are common signaling methods used throughout these SIA protocols. The CMX865A low-power wireline modem can be easily configured to perform these SIA protocols making it attractive for security panel applications. The purpose of this document is to describe how the CMX865A can be made to perform SIA communication protocols.

CMX865A: Motorola MC145443 to CMX865A Migration

CMX865A: Motorola MC145443 to CMX865A Migration

CMX865A Employed in Short Local Loops (SLL)

CMX865A Employed in Short Local Loops (SLL)

CMX865A - Tx V.23 FSK

Transmits FSK including a preamble. There is additional code for dialling and call progress. Works with the Rx FSK.pes file.

CMX865A - Rx V.23 FSK

A script that receives FSK including the preamble detection. There is additional code for the support of call progress. Works with the Tx FSK.pes file.

CMX865A - Reset to Operating

A simple script to reset the device and put it into operating mode.

CMX865A - Reset to Powersave

A simple script to reset the device and put it into powersave mode.

CMX865A - Programmable Tone Generators

Sets up the Programmable Tone Generators (PTG) to generate custom tones or simple melodies. A spreadsheet to calculate the required values, can be downloaded from the Knowledge Base Tab.

CMX865A - DTMF Decode

To Set the CMX865A into DTMF decode mode.

CMX865A - Ademco Contact ID

Audacity Project files for Ademco emulation.

CMX865A - Programmable Tone Decode

To set up the CMX865A Programmable Tone Detectors (PTD) for decoding the Ademco handshake and kissoff tones.

CMX865A - VoiceRecordandPlayback

Voice record and playback files using the CMX865A. Please refer to the Applications section of the datasheet.

CMX865A - Line State Detect

Uses the ADC in test mode to read the DC voltage across the line (snoop resistors required) to determine: "Line connected"/"not-connected" or "Line-in-use". Also contains a sub to reset the core to allow the method to be used with general modem function.

CMX86x: Tone Generator Calculator spreadsheet.

An Excel spreadsheet that calculates the values required for the Programmable Tone Generators. Single tones and dual-tones are allowed. The spreadsheet predicts the actual frequency and amplitude of each tone.

C-BUS Guides

Guides to operation and interfacing

Package: D4 (DW)

16-pin SOIC

Package: E4

16-pin TSSOP

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