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.
2004 CML Microsystems Plc
5
D/882/7
CMLMICRO [ CML MICROCIRCUITS ]
