Digital PMR Radio Processor
CMX7131/CMX7141
6.5.7 Tx Mode PRBS
In PRBS mode ($C1, Modem Control = $0032) the preamble and frame sync are transmitted automatically
followed by a PRBS pattern conforming to ITU-T O.153 (para. 2.1) giving a 511-bit repeating sequence.
6.5.8 Tx Mode Preamble
In Preamble mode ($C1, Modem Control = $0042) the preamble sequence [+3 +3 -3 -3] is sent continually.
This can be used to set up and adjust the RF hardware.
6.5.9 Tx Mode Mod Set-up
In Mod Set-up mode ($C1 = $0052) the output depends on the selected Tx modulation type. In two-point
mode, a repeating sequence of eight +3 symbols followed by eight -3 symbols is sent, and in I/Q mode a
continuous sequence of +3 symbols is sent. This can be used to set up and adjust the RF hardware.
6.5.10 Tx Mode Repeated Word
In Repeated Word mode ($C1 = $0062) the preamble and frame sync are transmitted automatically
followed by the data provided by the host in TxData4. This feature allows the NXDN standard test
waveforms to be transmitted as part of the test and qualification procedures.
6.5.11 Tx Sequencer
The Tx Sequencer provides an automated way of executing a sequence of actions, thus reducing timing
constraints placed on the host. It is controlled by setting b15 in the Modem Configuration register ($C7) to
1. If enabled, it will automatically start executing its sequence of transmit actions when the
CMX7131/CMX7141 is placed in Tx mode. The timing values for each action can be set in P3.75 to P3.79
and are defined in increments of 250µs.
The duration of the ramp by the RAMDAC is controlled by P3.80 – The RAMDAC scan time configuration.
It can be configured to ramp over a period of between 80µs and 32ms.
On expiry of the Tx ENA inactive delay the CMX7131/CMX7141 will return to the previous operating mode
automatically. It will also assert the “EndOfSequence” IRQ to the host at this point ($C6:b2 =1), signalling
that the Tx sequence has completed.
C-BUS latency delay
(10 – 260us)
CSN
Tx_ENA
P3.75
P3.79
Tx_ENA active
Tx_ENA inactive
DAC1
RAMDAC
P3.76
RAMDAC Up delay
P3.78
RAMDAC Down Delay
MOD1
Modulation
P3.77
Modulation Start Delay
End Of
Sequence
Tx Done
Figure 20 Automatic Tx Sequencer
2014 CML Microsystems Plc
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