CMX7163 QAM Modem
CMX7163
See:
10.1.8 I/Q Output Control - $5D, $5E write
10.1.9 I/Q Input Control - $5F, $60 write
10.1.21 I/Q Input Coarse Gain - $B1, $B2 write
10.1.23 I/Q Output Coarse Gain - $B4, $B5 write
10.1.22 I/Q Output Configuration - $B3 write
10.1.20 I/Q Input Configuration - $B0 write.
7.4.7 Tx Mode
In typical Tx operation, the preamble and FS1 or FS2 are transmitted automatically, and then data from
the Command FIFO is transmitted directly until a TxEnd command is processed or the mode is changed to
Rx or Idle. Data may be written to the Command FIFO prior to starting transmission, enabling the host to
create a buffer of data and therefore avoiding risk of the data running out during transmission. Further
buffering is provided to expand the amount of data that may be absorbed by the CMX7163.
The host should write the initial data to the Command FIFO and then set modem control to the required
transmit type with the Mode bits as Tx. As soon as the data has been read from the C-BUS TxData
registers the Cmd Done IRQ and/or Command FIFO IRQ will be asserted (when configured correctly).
More data should be loaded into the Command FIFO at this stage before data buffered in the CMX7163
runs out, otherwise an under-run will occur. To end the burst the host should send a TxEnd command,
signalling to the CMX7163 that the burst is to end, and the imminent data under-run is intentional.
It is possible to define a transmission sequence with defined RAMDAC ramp up/down, and GPIO on/off
events. The transmission sequence is configured using Program Block 5. For precise control of the instant
that transmission starts it is possible to trigger a transmission using GPIOA as an input. Selecting a Tx
mode with GPIOA configured as an “automatic input” places the device into a “Tx pending” state, where it
is neither receiving nor transmitting, just waiting for a trigger on GPIOA to begin transmission.
In general Figure 12 describes operation when a transmit sequence is defined by the host by:
Removing the need for the host to provide a ramp up – instead the configured Tx sequence will
deal with this
Inserting GPIO on/off events before ramp up and after ramp down as specified by the transmit
sequence.
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