Digital PMR Radio Processor
CMX7131/CMX7141
6.5.12 Rx Mode NXDN Formatted
In Rx mode the received signal should be routed through Input1. In NXDN Raw and Formatted modes the
CMX7131/CMX7141 will first search for frame synchronisation, and when this has been achieved the
following data is demodulated and supplied to the host through the RxData registers. A “DataReady” IRQ
indicates when each new block becomes available. The CMX7131/CMX7141 will continue demodulating
the input signal until the host resets the Mode bits to Tx or IDLE, or the modem detects the end of a call
and restarts the framesync search automatically.
6.5.13 Rx Mode Raw
Rx Mode Raw is included in this FI to facilitate BER measurements in I/Q mode. In this mode ($C1,
Modem Control = $0021), once a valid Frame Sync has been detected, all following data received is
loaded directly into the C-BUS RxData registers. This continues until the end of the burst (even if there is
no valid signal at the input). On exiting Rx Mode Raw, there may be a DataRdy IRQ pending which should
be cleared by the host. Note that Raw Mode operation always requires the incoming data to be preceded
with a valid Preamble and Frame Sync pattern in order to derive timing information for the demodulator.
The device will update the C-BUS RxData registers with Rx payload data as it becomes available. The
host MUST respond to the DataRDY IRQ before the RxData registers are over-written by subsequent data
from the modem.
6.5.14 Rx Mode Eye
In Rx 4FSK EYE mode ($C1 = $0031), the filtered received signal is output at the MOD1 pin as an ‘eye’
diagram for test and alignment purposes. A trigger pulse is output at the MOD2 pin to allow viewing on a
suitable oscilloscope. The trigger pulse is generated directly from the receiver xtal source, not from the
input signal. In I/Q mode, this includes I/Q dc calculation in RXDATA0, RXDATA1 and computed
Powersave Levels 1,2,3 in RXDATA2-4.
6.5.15 Rx Pass-through Mode
Rx Pass-through mode ($C1 = $0041) is very similar to Rx Mode Eye as described in section 6.5.14.
However the output at the MOD1 pin is the flat, unfiltered signal. A trigger pulse is output at the MOD2 pin
to allow viewing on a suitable oscilloscope. The trigger pulse is generated directly from the receiver xtal
source, not from the input signal.
Figure 21 Frequency Response for Rx Pass-through Mode
2014 CML Microsystems Plc
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