CML Microcircuits
COMMUNICATION SEMICONDUCTORS
CMX883
Baseband Processor for
‘Leisure Radios’
Advance Information
D/883/2 May 2002
Full-Feature Audio-Processing and Signalling for
Half Duplex FRS, MURS, GMRS and PMR446 ‘Leisure’ Radios
Features
•
Automatic signal 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
•
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
•
All call code and monitor modes for CTCSS
•
Selectable voice companding
•
XTCSS channel and data signalling
1.1
Brief Description
CMX883, 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 of this product offer, under software control,
increased functionality, versatility and privacy. Standard Extended-Code CTCSS and DCS 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.
With ultra low power requirements and graduated powersave, this product only requires a smaller, lower-
power µC than existing FRS/PMR446 solutions, is available in compact SSOP and TSSOP packages.
©
2002 CML Microsystems Plc
FRS Signalling Processor
CMX883
CMX883 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 CMX883 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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2002 CML Microsystems Plc
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D/883/2
FRS Signalling Processor
CMX883
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
The CMX883 is pre-programmed with 39 standard CTCSS (+ Notone and DCS ‘turn-off’ code) 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 CMX883 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.
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’ code being supplied from
the CTCSS facility. Decoding is carried out rapidly thus avoiding the loss of the beginning of speech or
data signals.
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2002 CML Microsystems Plc
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D/883/2
FRS Signalling Processor
CMX883
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 CMX883 has the ability to provide, independently
programmable, modulation outputs; for single or two-point modulation schemes.
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2002 CML Microsystems Plc
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D/883/2
FRS Signalling Processor
CMX883
CONTENTS
Section
1.0
1.1
1.2
1.3
1.4
Page
Features ........................................................................................................................1
Brief Description ............................................................................................................1
Block Diagram ...............................................................................................................7
Signal List......................................................................................................................8
External Components ..................................................................................................10
1.4.1 PCB Layout Guidelines and Power Supply Decoupling....................................11
1.4.2 Modulator Outputs...........................................................................................12
General Description .....................................................................................................13
1.5.1 Sleep Mode.....................................................................................................14
1.5.2 Auxiliary ADC..................................................................................................14
1.5.3 Receive Mode .................................................................................................15
1.5.4 Transmit Mode ................................................................................................22
1.5.5 XTCSS Coding................................................................................................25
1.5.6 C-BUS Operation ............................................................................................27
C-BUS Register Description.........................................................................................28
Application Notes.........................................................................................................44
Performance Specification...........................................................................................45
1.8.1 Electrical Performance ....................................................................................45
1.8.2 Packaging .......................................................................................................53
Page
Concurrent Rx Signalling Modes Supported by the CMX883........................................ 15
CTCSS Tones ............................................................................................................. 18
DCS Modulation Modes............................................................................................... 18
DCS 23 Bit Codes ....................................................................................................... 19
In-band Tones ............................................................................................................. 20
Concurrent Tx Modes Supported by the CMX883 ........................................................ 22
Page
1.5
1.6
1.7
1.8
Table
Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
Figure
Figure 1 Block Diagram..............................................................................................................7
Figure 2 Recommended External Components ........................................................................ 10
Figure 3 Power Supply Connections and De-coupling............................................................... 11
Figure 4 Modulator output components to achieve -100dB/decade roll-off ................................ 12
Figure 5 Rx Audio Filter Frequency Response.......................................................................... 16
Figure 6 De-emphasis Curve for TIA/EIA-603 Compliance ....................................................... 16
Figure 7 Low Pass Sub-Audio Band Filter for CTCSS and DCS ............................................... 17
Figure 8 25kHz Channel Audio Filter Response Template........................................................ 23
Figure 9 12.5kHz Channel Audio Filter Response Template..................................................... 23
Figure 10 Audio Frequency Pre-emphasis Template ................................................................ 24
Figure 11 C-BUS Transactions................................................................................................. 27
Figure 12 Possible FRS Configuration...................................................................................... 44
Figure 13 C-BUS Timing .......................................................................................................... 52
Figure 14 Mechanical Outline of 28-pin SSOP (D6): Order as part no. CMX883D6 ................ 53
Figure 15 Mechanical Outline of 28-pin TSSOP (E1): Order as part no. CMX883E1............... 53
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2002 CML Microsystems Plc
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D/883/2
