FRS Signalling Processor
CMX882
1.5
General Description
The CMX882 is intended for use in half duplex analogue two way land mobile radio (LMR) equipment and
is particularly suited to enhanced MURS / GMRS / FRS with GPS terminal designs. The CMX882
provides radio signal encoder and decoder functions for: Voice, in-band tones, XTCSS, CTCSS, DCS
and FFSK/MSK data permitting simple to sophisticated levels of tone control and data transfer. Power
control facilities allow the device to be placed in varying levels of sleep allowing the user to fine tune the
power depending on system requirements. The CMX882 includes a crystal clock generator, with buffered
output, to provide a common system clock if required. A block diagram of the CMX882 is shown in
Figure 1.
Tx functions
Audio
o
o
o
o
o
o
Single/dual microphone inputs with input amplifier and programmable gain adjustment
Filtering selectable for 12.5kHz and 25kHz channels
Selectable pre-emphasis
Selectable compression
Selectable frequency inversion voice scrambling
2-point modulation outputs with programmable level adjustment
Signalling
o
o
o
o
o
Pre-programmed 51 tone CTCSS encoder
Programmable 23/24bit DCS encoder
Programmable audio tone generator (for custom audio tones)
Pre-programmed XTCSS and in-band tone encoder
1200/2400bps MSK data packet encoder (suitable for text messaging/paging, caller
identification, caller location, digital poll of remote radio location, GPS information via
NMEA 0183 data transfer etc.), incorporating interleaving, FEC, CRC and data scrambler
Rx functions
Audio
o
o
o
o
o
o
Single/dual demodulator inputs with input amplifier and programmable gain adjustment
Voice-band and sub-audio rejection filtering
Selectable de-emphasis
Selectable expansion
Selectable frequency inversion voice de-scrambling
Software volume control
Signalling
o
o
o
o
1 from 51 CTCSS decoder + Tone Clone mode
23/24bit DCS decoder
Pre-programmed in-band tone decode with XTCSS 4 tone addressing
1200/2400bps MSK data packet decoder with automatic bit rate recognition, 16 bit frame
sync detector, error correction, data de-scrambler and packet disassembly
Signal Monitor (RSSI / Microphone / Rx channel level monitor)
o
2004 CML Microsystems Plc
14
D/882/7
CMLMICRO [ CML MICROCIRCUITS ]
