CMX7163 QAM Modem
CMX7163
Figure 23 Normalised
Constellation (even with a
frequency or phase error)
Figure 24 Normalised
Constellation (noisy received
signal)
Note: The images of receive diagnostic modes shown above are idealised. In practice when using the I
Output and Q Output signals to view diagnostics the transitions between constellation point are not
instantaneous. Using an analogue oscilloscope is the best way to observe these diagnostic signals.
See:
10.1.18 Modem Mode and Control - $6B write
10.1.10Signal Control - $61 write.
7.4.13 Data Transfer
The payload data is transferred to and from the host via the C-BUS Command and Rx Data FIFOs, each
of which provide efficient streaming C-BUS access. FIFO fill level can be determined by reading the
Receive FIFO Level and Modem Command FIFO Level and controlled using FIFO Control - $50 write
register. Interrupts may be provided on FIFO fill thresholds being reached, or successful transfer of a block
of host requested FIFO data between CMX7163 modem and FIFOs.
Each FIFO word is 16 bits, with the least significant byte (LSByte) containing data, and the most significant
(MSByte) containing control information. The control information indicates to the CMX7163 what type, or
how much data is in the LSByte, for example if the byte belongs to a header block or contains only 4 valid
bits. The control and data bytes may be written or read together using the Receive FIFO Word and Modem
Command FIFO Word registers, or individually using their byte-wide registers.
Word wide FIFO writes involve writing 16-bit words to the Modem Command FIFO Word register using
either a single write or streaming C-BUS. The whole word written is put into the Command FIFO, with the
upper byte interpreted as control and the lower byte as data. This causes the control byte to be held in the
Command FIFO Control Byte register.
Byte wide FIFO writes involve writing to the Modem Command FIFO Data Byte register using either single
access or streaming C-BUS. This causes the Modem Command FIFO Control Byte (MSByte) and data
written to the Modem Command FIFO Data Byte (LSByte) registers to be put into the command FIFO as
one word. The control byte can be written separately as a single byte (this does not result in anything being
added to the FIFO) or is preserved from a previous 16-bit Modem Command FIFO Data Byte write.
Likewise a word read from the Rx Data FIFO will return the Receive FIFO Control Byte in the MSByte and
the Receive FIFO Data Byte at the top of the FIFO in the LSByte. Both registers will be updated so that
when read next time they will provide details of the next item in the FIFO. Reading the Receive FIFO
Control Byte only will not change the FIFO content. Reading the Receive FIFO Data Byte only will provide
the data and remove the item from the FIFO – updating both control and data registers. In summary:
Operation
Effect
write Modem Command
FIFO Control Byte
register
Cmd FIFO control word updated, nothing added to Cmd FIFO
write Modem Command
FIFO Data Byte register
write Modem Command
FIFO Word register
read Receive FIFO
Control Byte register
Cmd FIFO control word + data byte written are added to Cmd FIFO
data word (control and data bytes) is added to Cmd FIFO.
Cmd FIFO control word updated for future writes.
Rx FIFO control word is returned, no effect on Rx FIFO contents
2014 CML Microsystems Plc
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