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Baseband Processor IC with GPS Data Signalling for FRS, MURS, PMR446 and GMRS 'Leisure Radios'



  • Automatic Signal Scanning; 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 using XTCSS
  • 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
  • Half-Duplex 1200/2400 bps FFSK/MSK Modem
  • Selectable Data Scrambling
  • Robust Automatic Packet Data Protocol with:
    • Error Correction and Detection
    • Interleaving and Data Scrambling/Privacy


  • FRS, MURS, PMR446 and GMRS 'Leisure' Radios
  • FRS Text Messaging

Supply Requirement:

  • 2.7 to 5.5 V

CMX882, a full-function half-duplex audio and signalling 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 in this product offer, under software control, increased functionality, versatility and privacy.

Standard Extended-Code CTCSS and DCS functions are 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.

For advanced and enhanced radio operation the CMX882 embodies a 1200/2400 bps freeformat and formatable packet data FFSK/MSK modem (compatible with NMEA 0183) for Global Positioning by Satellite (GPS) operations.

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:

All Call Code – transmissions using this code will be heard by all CMX882 enhanced radios regardless of their selected CTCSS code. This provides an important benefit to both safety and convenience.

All Codes Monitor – selection of this code at the receiver enables all transmissions that are using a CTCSS tone to be heard, and the tone number to be reported. Open channel noise or calls lacking coding will go unheard.

This is a superior method of ‘channel monitoring’ which allows miscoded calls from conventional CTCSS-party radios to be heard and directly responded to.

With ultra low power requirements and graduated powersave, this product only requires a smaller, lower-power µC than existing FRS/PMR446 solutions, and is available in compact SSOP and TSSOP packages.

XTCSS Signalling
A state-of-the art (squelch) signalling format, employing both sub-audio (CTCSS) and in-band (XTC) signalling concurrently, which offers more than twice as many privacy codes as standard CTCSS operation; and completely eliminates interference caused by other traffic on the channel (quiet operation).

Additionally the XTCSS signalling can be employed as on over-air control for such features as voice-scrambling and voice-compression.

XTCSS is fully compatible with both conventional and enhanced CTCSS signalling operations and will implement the ‘All Call Code’ and ‘All Codes Monitor’ functions.

Data for GPS
The CMX882 facilitates Global Positioning by Satellite (GPS) by providing, in the Tx path, a 1200/2400 bps MSK data packet encoder (suitable for NMEA 0183 data transfer) incorporating interleaving, FEC, CRC and data scrambling.

In the Rx path a 1200/2400 bps data packet decoder with automatic bit-rate recognition, 16-bit frame-sync detector, error correction, data de-scrambling and packet disassembly is available.

Block Diagram


Design Support Information

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).
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