Marine VHF Audio and Signalling Processor
CMX885
6
General Description
The CMX885 is intended for use in half duplex analogue two-way mobile radio equipment and is
particularly suited to the Marine VHF band. The CMX885 provides signal filtering, encoder and decoder
functions for audio, inband tones, DTMF, NWR and DSC/ATIS, permitting simple to sophisticated levels of
tone control and data transfer. A flexible power control facility allows the device to be placed in its
optimum powersave mode when not actively processing signals.
The CMX885 includes a crystal clock generator, with a buffered output, to provide a common system
clock if required. A block diagram of the CMX885 is shown in Figure 1.
The signal processing blocks can be individually assigned to either of two signal processing paths, which
in turn, can be routed from any of the three audio/discriminator input pins. This allows for a very flexible
routing architecture and allows the facility for different processing blocks to act on different analogue
inputs.
For Marine use, it would be typical to route Rx Audio from the working channel receiver through from the
DISCN input, while at the same time routing the DSC/ATIS FSK modem from the DSC channel 70
receiver from the ALTN input.
Tx Functions:
o
o
o
o
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 frequency inversion voice scrambling
Selectable audio processing order
Two-point modulation outputs with programmable level adjustment
Programmable audio tone generator (for custom audio tones)
Programmable DTMF generator
Tx Enable output
1200bps FSK modem for DSC/ATIS use (to ITU-R M.493-11)
Rx Functions:
o
o
o
o
o
o
o
o
o
o
Single/dual demodulator inputs with input amplifier and programmable gain adjustment
Audio-band and sub-audio rejection filtering
Selectable de-emphasis
Selectable frequency inversion voice de-scrambling
Selectable audio processing order
Software volume control
DTMF decoder
Rx Enable output
1200bps FSK modem for DSC/ATIS use (to ITU-R M.493-11)
NWR SAME and WAT detector
Auxiliary Functions:
o
o
o
2 programmable system clock outputs
2 auxiliary ADCs with selectable input paths
4 auxiliary DACs, one with built-in programmable RAMDAC
Interface:
o
o
C-BUS, 4 wire high speed synchronous serial command/data bus
Open drain IRQ to host
© 2010 CML Microsystems Plc
13
D/885/3
CMLMICRO [ CML MICROCIRCUITS ]
