Digital PMR Radio Processor
CMX7131/CMX7141
Auxiliary Functions:
Two programmable system clock outputs
Two auxiliary ADCs with four selectable external input paths
Four auxiliary DACs, one with built-in programmable RAMDAC
Two RF PLLs (CMX7131 only)
Interface:
Optimised C-BUS (4 wire high speed synchronous serial command/data bus) interface to host for
control and data transfer
Open drain IRQ to host
SPI bus interface for speech codec to support the AMBE+2 vocoder
Two GPIO pins
Serial Memory boot mode
C-BUS (host) boot mode
Auxiliary C-BUS interface to CMX994 Direct Conversion Receiver
5.2 System Design
System architecture supports an external vocoder, implementing the AMBE+2 algorithm, such as the
AMBE-3000TM or as part of the host uC implementation using SPI-Codec mode, in which the
CMX7131/CMX7141 acts as an external audio codec attached to the vocoder. The host must issue all
control commands to the vocoder and also transfer coded data packets between the vocoder and
CMX7131/CMX7141. The device will automatically enable/disable the activity on the SPI-Codec port when
a voice call is in progress.
In SPI-Codec mode, signed 16-bit linear PCM audio samples are transferred at 8ksps. When this mode is
selected:
In Tx: the CMX7131/CMX7141 microphone input should be routed from MIC to Input2. This signal is
lowpass filtered, converted to PCM data and then output on the EPSI pin of the SPI-Codec port for
the external vocoder to process.
In Rx: the CMX7131/CMX7141 AUDIO output should be routed from Output1. PCM data samples are
read from the EPSO pin of the SPI-Codec port, then filtered and output via the audio output
attenuator.
VOC_DIS
0
SPI-Codec Port mode
SPI
activity
1
SPI Port enabled during Rx or Tx, PCM data from MIC/to
AUDIO passed over SPI bus
The automatic enable/disable of the SPI-Codec port during Rx and Tx may be overridden by setting the
VOC_DIS bit in the Modem Configuration register, $C7:b7. In this situation, the activity on the SPI-Codec
port is determined by the host setting/clearing the SPI-Codec ENA, $B1:b0.
VOC_DIS
SPI-Codec Port mode
activity
1
1
0
1
SPI
SPI
SPI Port disabled
SPI Port enabled, PCM data from MIC/to AUDIO passed over
SPI bus
5.2.1 Vocoder Implementation
All payload data (including voice traffic channel data) is routed through the main C-BUS to the host. The
host can then transfer it to/from the vocoder over a suitable port supported by the chosen vocoder.
Typically vocoders do not include audio Digital-to-Analogue and Analogue-to-Digital converters, so the
2014 CML Microsystems Plc
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CMLMICRO [ CML MICROCIRCUITS ]
