PMR Signalling Processor
CMX881
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.
Selcall
This product implements a fully programmable Selcall encoder and decoder employing normal and
special tones. Tone frequencies, decoder bandwidths and thresholds are programmed by the host µC. In
receive the CMX881 scans its internal tone table for a match, reporting its results to the µC.
FFSK/MSK Data
An MPT packet and free-format half duplex FFSK/MSK modem is implemented. In receive this device
can decode data at either automatic or manually selected 1200b/s or 2400b/s rates. Additionally, in
receive, a 16-bit programmed frame sync (MPT packet-type) pattern can be detected. Formatting control
and data transfers to and from the modem is under the control of the host µC.
DTMF Tx
The CMX881, under µC control, can generate and transmit all standard DTMF tone-pairs.
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 CMX881 has the ability to provide, independently
programmable, modulation outputs; for single or two-point modulation schemes.
2004 CML Microsystems Plc
4
D/881/7
CMLMICRO [ CML MICROCIRCUITS ]
