CML Microcircuits
COMMUNICATION SEMICONDUCTORS
CMX882
Baseband Processor for
‘Leisure’ Radios with Data
Provisional Issue
D/882/7 March 2004
Full-Feature Audio-Processing, Signalling and GPS Data for
Half Duplex FRS, MURS, PMR44 and GMRS ‘Leisure’ Radios
Features
•
Automatic signal type scanning and IRQ on
detection of valid Rx signals, level or RSSI
•
Tone generator for caller recognition tunes
•
Programmable power down control
•
Programmable signal detection thresholds
•
Low Power operation with Zero Power mode
•
Uncommitted Aux ADC with switchable input
to monitor signals
•
Silent operation by removal of unwanted calls
•
Selectable voice companding
•
Voice processing facilities, including Tx and Rx
gain setting and voice/subaudio filtering
•
C-BUS serial host interface
•
RF interface allowing 1 or 2 point modulation
•
Programmable soft limiter
•
Enhanced CTCSS and 23/24 bit DCS codecs
•
Zero ‘talk down’ CTCSS decoder performance
prevents dropouts
•
‘All call code’ and ‘monitor’ modes for CTCSS
•
Audio scrambling
•
Robust Half Duplex FFSK/MSK modem,
1200/2400 bps, gets data through when signal
is too degraded for voice – for text
messaging/paging, location transfer, etc.
applications.
•
XTCSS channel and data signalling
•
Robust automatic packet data protocol with:
Error correction and detection, Interleaving
and data scrambling/privacy coding.
2004 CML Microsystems Plc
FRS Signalling Processor
CMX882
1.1
Brief Description
CMX882, a full-function half-duplex audio and signalling processor IC for FRS and PMR446 type facilities
suitable 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 functions are
integrated with the new XTCSS code implementation. XTCSS provides additional and improved 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 provides a 1200/2400 bps free-format and
packet data FFSK/MSK modem for text messaging/paging, passing GPS location data (compatible with
NMEA 0183) and other data applications.
With ultra low power requirements and graduated powersave, this product only requires a smaller, lower-
power µC than existing FRS/PMR446 solutions. It is available in compact SSOP and TSSOP packages.
2004 CML Microsystems Plc
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D/882/7
FRS Signalling Processor
CMX882
CMX882 Functions and Facilities
Half Duplex Operation
Working in a half duplex mode, when the product is in Tx the Rx sections can be powered down to
extend battery life, conversely in Rx major sections of the Tx can be treated in the same manner.
Serial Control and Data Interfaces
C-BUS: Serial control, data and command program interface compatible with SCI, SPI and Microwire
type interfaces.
Power Requirements and Economy
With an ultra low power requirement, the CMX882 operates from a single 2.7 to 3.6 Volt supply with
graduated ‘Sleep Mode’ powersaving facilities for both Rx and Tx modes.
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FRS Signalling Processor
CMX882
Signalling:
XTCSS
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 an over-air control for such features as voice-
compression. XTCSS is fully compatible with both conventional and enhanced CTCSS signalling
operations and will implement the
All Call Code
function.
CTCSS
’Zero talkdown’ performance eliminates unwanted breaks in communication. The CMX882 is pre-
programmed with 39 standard CTCSS (+ Notone and DCS ‘turn off’ tone) and 12 additional ‘split-tone’
frequencies. Any one of these can be selected for reception or transmission. Decoding is aided by the
use of adjustable decode bandwidths and threshold levels. Decoding is carried out rapidly thus avoiding
the loss of the beginning of speech or data signals. A CTCSS configuration of this product enables ‘Tone
Cloning’.
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.
2004 CML Microsystems Plc
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D/882/7
FRS Signalling Processor
CMX882
DCS
The DCS code is in NRZ format and is transmitted at 134.4b/s in either 23 or 24 bit patterns. The code,
for transmission or reception is programmed via the host µC with the ‘turn off’ tone being supplied from
the CTCSS facility. Decoding is carried out rapidly thus avoiding the loss of the beginning of speech or
data signals.
FFSK/MSK Modem
This high performance modem facilitates data transfers (e.g. text messaging/paging caller identification,
caller location, digital poll of remote radio location, GPS information, etc.) by providing a 1200/2400 bps
MSK data packet encoder (suitable for NMEA 0183 data transfer). Software selectable interleaving, error
correction (FEC), error checking (CRC) and data scrambling functions provide multiple communication
types to select from robustness, speed and privacy options. In the Rx path, a 1200/2400 bps data packet
decoder features automatic bit-rate recognition, 16-bit frame-sync detector, error correction and checking,
data de-scrambling and packet disassembly. High performance allows the modem to be used even when
radio link quality is too degraded for voice communications.
Modulation type is optimised to maximise robustness and data rate and simplify hardware connections to
voice radio Tx and Rx circuits with virtually no modification. The modulation type also is appropriate to
develop F2D type emissions, as required by certain regulations. (F2D = frequency modulation, digital
modulation with modulated subcarrier, transmitted information is data/telemetry/telecommand).
Signal Monitor
An auxiliary circuit intended for the monitoring of any signal or level; both internal and external. This
function can be used in conjunction with the host µC to allow such activities as: VOX operation and/or the
‘wake-up’ of powered-down circuitry.
Audio Processing:
Adjustable Gain Input Amplifiers
Selectable, component adjustable inputs are available for microphone or line voiceband or discriminator
inputs. In either mode (Tx or Rx) the selected input can be further level adjusted under the control of the
host µC prior to signal or audio- processing.
Voiceband and Sub-Audio Filtering with Limiting
Both Rx and Tx paths present voiceband filtering; the Tx path filter can be configured to either 12.5 or 25
kHz channel spacing whilst the Rx path also includes a sub-audio passband filter.
Voiceband Pre-emphasis and De-emphasis
Voiceband pre-emphasis is selectable to either 12.5 or 25 kHz channel configurations in the Tx path; de-
emphasis at -6dB/ octave is selectable in the Rx path.
Software Adjustable Gains, Volume, Mixing and Routing
Providing total flexibility of operation, this product, under µC control has the ability to select and route
functions and audio and signal paths, set bandwidths and threshold levels, mix audio and sub bands and
vary both input and out gain/attenuation levels. Output levels from all analogue ports can be ‘ramped’ up
and down at independently programmed rates.
Attenuation-Adjustable Single/Two-Point Modulation Outputs
To facilitate a wide range of transmitter types, the CMX882 has the ability to provide, independently
programmable, modulation outputs; for single or two-point modulation schemes.
Scrambler
An optional frequency inversion scrambler is provided in both transmit and receive modes.
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