Product description

The CMX883, a full-function half-duplex audio and signalling baseband processor IC for FRS and PMR446 type facilities for both complex and simple end-designs.
Under the control of the host µC, all voiceband requirements are catered for:
Voiceband and sub-audio filtering, pre/de-emphasis, compression and expansion and audio routing and global level setting with single or two-point modulation in the transmit path.

The combination of new and standard signalling functions of this product offer, under software control, increased functionality, versatility and privacy.
Standard Extended-Code CTCSS and DCS is integrated with the new XTCSS code implementation. XTCSS provides more and better squelch-centred privacy codes with the added advantage of ‘silent operation’; no annoying interference from other sub-audio users.
XTCSS fitted radios enjoy more privacy and flexibility of operation. The CTCSS configuration of this product enables ‘Tone Cloning’.

Additionally two unique features of this product are its CTCSS ‘All Call Code’ and ‘All Codes Monitor’ modes.

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  • Automatic Signal Scanning and IRQ on Detection of Valid Rx Signals
  • XTCSS Channel and Data Signalling
  • Tone Generation for Caller Recognition Tunes
  • Low Power Operation with Graduated Powersave
  • Programmable Signal Detection Thresholds
  • Aux ADC Available to Monitor Inputs
  • Quiet-Operation by Removing Unwanted Calls
  • Selectable Voice Companding
  • Voice Processing Facilities:
    – Tx and Rx Path Gain Setting
    – Voiceband and Sub-Audio Filtering
  • Programmable Soft Limiter
  • C-BUS Serial Host Interface
  • Tx Interface for Single or Two-Point Modulation
  • Enhanced CTCSS and DCS (23/24-bit) Codecs All-Code and Monitor-Mode for CTCSS
  • Robust Automatic Packet Data Protocol with:
    – Error Correction and Detection
    – Interleaving and Data Scrambling/Privacy


  • FRS, MURS, PMR446 and GMRS ‘Leisure’ Radios

Power supply requirement

  • 2.7 to 3.6 V

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Design resources

CMX882 Pseudo Code Implementation

The CMX882 is a sophisticated modem + baseband processor targeted at “family radio” applications (e.g. FRS/GMRS/MURS/PMR446 radios). It is particularly well suited to family radios that include facilities for text messaging and GPS location data exchange. The purpose of this application note is to illustrate how the CMX882 can be configured for a feature-rich “family radio” product.

HSC and XTCSS Coding for Radio and Paging Systems

The Hexadecimal Sequential Code (HSC) is a coding format for sequential tone signalling systems. HSC permits address codes, instruction codes and data blocks to be exchanged on an unrestricted basis between all units in a network, thus providing the key to the design of fully integrated base/mobile/personal communications schemes. HSC is also compatible with the frequencies and protocols used for international '5-tone' selective call (SelCall).

C-BUS Guides

Guides to operation and interfacing

Variable Split-Band Scrambling

How it works

Package: E1

28-pin TSSOP

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