Product description

The CMX7262 Professional Radio Vocoder IC is a device supporting Tri-Wave Excited Linear Prediction (TWELP) vocoder, utilising CML’s FirmASIC technology.

TWELP is the latest state-of-the-art vocoder technology providing high- quality natural sounding voice and good reproduction of non-voiced signals such as: police, fire and ambulance sirens.

Input and output signals are passed through the C-BUS interface or the on-chip analogue-to-digital and digital-to-analogue converters (ADC/DAC).

The Function Image can be loaded automatically from a host µC over the C-BUS or from an external memory device. The Function Image upgrade releases can enhance the devices functions and features.

The CMX7262 operates from a 3.0V to 3.6V supply and includes power saving modes. It is available in a 64-VQFN (Q1) and 64-LQFP (L9) packages.

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Devices are available through our distributors below:


  • SalesNetworkLogo_2
  • Mouser_logo
  • RFMW logo

Block diagram



  • Half-duplex Operation
  • FEC Built-in
  • Noise Reduction
  • No External DSP or Codecs Required
  • Choice of Signal Input/Out Sources
  • No royalty/license fee
  • C-BUS Host Serial Interface
    – SPI-like with Register Addressing
    – Streaming Input/Output Registers, Low Host Latency
    – C-BUS/Host, PCM Codec, Analogue Audio Output
  • Auxiliary Functions
    – GPIOs
    – Analogue Input/Output Multiplexer
  • Low Power 3.3V Operation with Powersave Functions
  • Small 64-pin VQFN and 64-LQFP (L9) Packages


  • Digital Radio Systems
  • Personal Area Networks
  • Secure Digital Voice Comms
  • Wireless PBX
  • VoIP Applications
  • Digital Software Defined Radio (SDR)

Power supply requirement

  • 3.0 to 3.6 V

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Design resources


Q.  Should pull-up or pull-down resistors be connected to CMX7262 device GPIO pins (GPIOA, GPIOB, GPIOC, and GPIOD)?

A.  The CMX7262 features flexible GPIO pins that can be independently configured via C-BUS serial interface commands to operate in one of the following modes: CMOS digital output, CMOS digital input or CMOS digital input with bus hold. Bus hold automatically engages a 75kohm internal pull-up or pull-down resistor that reinforces the current logic state of the input signal. As is normally the case, the state of a CMOS digital input will be indeterminate and may increase device supply current when the input’s voltage is not at valid ‘0’ or ‘1’, i.e. when the node voltage is “floating.”

When the CMX7262 is RESET (by asserting its RESETN pin, issuing a C-BUS General RESET or by triggering an internal power on reset) all its GPIO pins are immediately placed in CMOS digital input mode. Any GPIO pins not being pulled either up or down by an external load will be floating. Once a Function Image™ is loaded into the device then all its GPIO pins are placed in CMOS digital input with bus hold.

If user circuits require one or more GPIO pins to be held at a deterministic ’0’ or ‘1’, i.e. not floating after RESET and before the Function Image™ is loaded then that circuit should connect external pull-up or pull-down circuits to such pins.

CMX7262 - Configuring and optimising a set up for the evaluation of speech

Configuring and optimising a set up for the evaluation of speech using the CMX7262 TWELP Vocoder.

Evaluation Kits

PE0003 PE0003 The PE0003 Evaluation Kit Interface Card is a global interface system for use with evaluation kits for CML’s new generation ICs, including FirmASIC™ based products. This greatly simplifies the approach to the evaluation and design-in process. PE0003_Product_Page
PE0601-7262 PE0601 The PE0601 Platform Evaluation Kit is designed to assist in the evaluation and application development of the CMX7x6x range of FirmASIC products. The kit is in the form of a populated PCB comprising a CMX7x6x target IC and appropriate supporting components and circuitry. PE0601_Product_Preview


C-BUS Guides

Guides to operation and interfacing

PE0601-7261-7262 Board Schematics



CMX7262 Thick Stub

PE0602-7262 Quick Start

A simple guide to help users get started evaluating the CMX7262 TWELP Vocoder using the PE0602-7261. A PE0003 or a processor development kit with an SPI interface is required for control.

PE0601-7262 - Encode and Decode from Disk - a script pair for encoding and decoding TWELP

Encode2dsk.pes encodes audio into TWELP frames and store them on the PC disk. The length of the recording is set in frames. The FEC mode can be toggled and frame size can be set to all possible values. The script opens a text file to which it writes the settings so that the decode script settings are correctly set. Decode_from_disk.pes takes the pre-recorded TWELP frames from the PC disk and decodes them to audio. The length of the recording is determined by the number of recorded frames saved to disk by the encode script. Options in both scripts allow for different input sources and different outputs.

Package: Q1

64-pin VQFN

Package: L9

64-pin LQFP

VQFN Design Guidance Notes

VQFN Design Guidance Notes

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