Baseband Processor For Mixed Mode Land Mobile Radio
CMX880
Auto Detect Mode:
The CMX880 has two receive phases; (1) signal type identification and (2) continuous signal processing. Phase
1 monitors the incoming signal and identifies the signal type, if that type has been enabled. Following signal type
identification, phase 2 processes the incoming signal in accordance with the identified signal type. The Auto
Detect Mode bit controls the action following identification of a signal type.
Bit 8
0
Mode 0: CMX880 will process the detected signal and
also continue searching for the presence of other enabled
signal types. If a second signal type is found this also will
be processed by the CMX880.
1
Mode 1: CMX880 will process the detected signal and
cease searching for other signal types. Selcall is
excluded from this mode.
Mode 0 can be used for processing analogue ‘in-band’ data signalling, allowing sub-audio detection to be
followed by Selcall or FFSK detection and processing. Mode 0 can cause the CMX880 to become overloaded if
too many signal types are enabled. Voice processing is not affected by the Auto Detect Mode bit.
C4FM processing requires the full capacity of the CMX880. If C4FM is enabled, the CMX880 must be placed in
Mode 1 either before enabling receive mode (bit 0) or immediately after detection of a C4FM signal.
If additional signalling schemes need to be enabled after auto detection in mode 1, these can be individually
enabled by setting the appropriate bits in the ‘RECEIVE MODE CONTROL’ register, including the detected
scheme, and setting the Auto Detect Mode bit to ‘0’.
Voice Filter Control:
The voice filter control bits determine the filter mode applied to the voice signal before it is output to the ‘Audio’
port. De-emphasis can be applied without other filtering by setting bits 7, 6, 5 = 0, 0, 1.
Bit 7
Bit 6
Bit 5
0
X
0
1
1
1
0
X
1
0
1
1
0
1
X
X
0
1
No filtering.
Enable de-emphasis.
12.5kHz channel filtering.
25.0kHz channel filtering.
APCO 25.
Reserved – do not use.
ã 2001 Consumer Microcircuits Limited
55
D/880/1
CMLMICRO [ CML MICROCIRCUITS ]
