Product description

The CMX148 PMR audio and data processor is a half-duplex, signalling and data processing IC for use in systems that utilise the host µC to perform signalling, including CTCSS/DCS encoding/decoding. Comprehensive audio processing facilities include: complete audio processing, filtering, companding, pre or de-emphasis and frequency inversion scrambling.

Signal routing and filtering is included to assist host µC based signal encoding/decoding applications.

A DTMF encoder/decoder, a full complement of auxiliary ADCs and DACs and dual synthesised clock outputs are included in this low power PMR processor.

The device also has flexible powersaving modes and is available in 48-pin VQFN and LQFP packages.

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Block diagram


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  • Concurrent Audio/ Signalling/Data Operations
  • Complete Audio-band Processing:
    – Selectable Audio Processing Order
    – Pre and De-emphasis
    – Selectable 2.55/3.0 kHz Filtering
    – Selectable Audio Highpass Filter Cut-off
    – Compandor
    – Limiter
  • Programmable Voice Scrambler
  • MSK/FFSK Data Modem with Packet or Freeformat Modes with FEC, CRC, Interleaving and Scrambling
  • DTMF and Audio Tone Encoder/Decoder
  • Sub-audio Signalling Filters for CTCSS and DCS
  • Routing for Host µC Signalling
  • Dual Auxiliary ADC with Four Multiplexed Inputs
  • Four Auxiliary DACs
  • Dual Programmable System-Clock Outputs
  • Tx Outputs for Single, Two-point or I/Q Modulation
  • Microphone and Discriminator Analogue Inputs
  • Digital Gain Adjustment/s
  • C-BUS Serial Interface to Host µC
  • Flexible Powersave Modes


  • Professonal PMR
  • Leisure Radio Systems:
    – PMR, FRS, MURS, PMR446 and GMRS

Power supply requirement

  • 3.0 to 3.6 V

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Design resources

CMX148 - Transmit CTCSS and Processed Voice

Transmit externally generated CTCSS and processed voice. Input a 250.3Hz tone at 62mVrms at SIG. Observe 250.3Hz CTCSS tone at MOD1 output mixed with the processed voice signal input at MIC.

CMX148 Transmit CTCSS and DTMF

Transmit externally generated CTCSS and DTMF. Input a 250.3Hz tone at 62mVrms at SIG. Observe DTMF and CTCSS at MOD1, CTCSS only at MOD2. DTMF encoder is set to typical level with -2dB twist applied to the lower tone. DTMF is a repeating sequence of 4 digits (‘1’, ‘5’, ‘9’, ‘0’), 50ms on, 50ms off, repeating after 1s.

CMX148 Receive CTCSS, DTMF and Voice

Receive CTCSS, DTMF + voice. Input a DTMF and a CTCSS signal at DISC in. Observe detected DTMF codes in script output window. The Audio output is enabled and the filtered input signal (to remove DTMF) is output. Observe CTCSS signal with DTMF signal filtered at MOD2.

CMX148 - Transmit CTCSS and FFSK Format 2

Transmit externally generated CTCSS and FFSK Format 2. Input a 250.3Hz tone at 62mVrms at ALT. Observe FFSK and CTCSS at MOD1, CTCSS only at MOD2. FFSK transmission is a format 2 frame consisting of 10 data bytes. Frame head; address byte: 0xa1, Information byte: 0x21. Data; 0x5125, Data; 0x4e29, Data; 0x9020, Data; 0x056f, Data; 0x9dff

CMX148 - Receive CTCSS, FFSK (Format 2) and Voice

Receive CTCSS, FFSK (Format 2) and Voice. Input a FFSK and a CTCSS at DISC in. The expected message format is type 2 with the frame head address byte set to 0xa1. Observe received data in script output window. Ten data bytes per frame are expected. The first RxData1 and RxData2 values are the frame head. The Audio output is enabled and the filtered input signal (with CTCSS removed) is output. Observe CTCSS signal (FFSK signal removed) at MOD2. PE0003 LED2 is lit during frame reception.

CMX148 Receive CTCSS and Voice

Receive CTCSS and processed voice. Input a processed voice with sub-audio at DISC in. Observe clear voice at Audio output and CTCSS signal at MOD2.

C-BUS Guides

Guides to operation and interfacing

Variable Split-Band Scrambling

How it works

Package: Q3

48-pin VQFN

Package: L4

48-pin LQFP

VQFN Design Guidance Notes

VQFN Design Guidance Notes

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