Product description

The CMX881 is a full-function half-duplex audio and signalling baseband processor IC for both PMR and trunked radio systems and is implementable to 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 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 Code CTCSS and DCS functions and selcall operation.

To cater for call setup and system signalling the CMX881 offers an embedded 1200/2400 bps MSK/FFSK freeformat modem with sync detection in the Rx path and MPT standard CRC operations in Tx/Rx modes.

With ultra low power requirements and graduated powersave, this product therefore requires a smaller, more low-power µC than existing PMR or trunked radio systems, is available in compact SSOP and TSSOP packages.

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Devices are available through our distributors below:



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Block diagram


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  • Automatic Signal Scanning and IRQ on Detection of Valid Rx Signals
  • Tone Generation for Caller Recognition Tunes
  • Programmable Signal Detection Thresholds
  • Aux ADC Available to Monitor Inputs
  • Programmable Selcall Codec
  • Meets ETS 300 086, MPT1327, PAA and ETS 300 230 Specs
  • 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


  • PMR Radio Systems
  • Trunked Radio Systems
  • Wireless Signalling

Power supply requirement

  • 2.7 to 5.5 V

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Design resources

C-BUS Guides

Guides to operation and interfacing

Package: D6

28-pin SSOP

Package: E1

28-pin TSSOP

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