CMX869 View Datasheet(PDF) - CML Microsystems Plc
Part Name
Description
MFG CO.
'CMX869' PDF : 46 Pages View PDF
Low Power V.32 bis Modem
CMX869
6.5 QAM Modem Command Register
QAM Modem Command Register: 16-bit write-only. C-BUS address $EA
Bit: 15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
0
Command
Protocol/Bit Rate
The V.22, V.22 bis, V.32, V.32 bis QAM modem is controlled by writing the commands listed below to
this register. B15-6 should all be cleared to 0. These commands will not take effect unless both Tx and
Rx Mode Registers have both been set to QAM modem mode. This register should only be written to
when b13 (Programming Flag bit) of the Status Register is 1.
Bit: b5 b4 b3 b2 b1 b0 Command
0 0 0 0 0 0 Stop modem
F 0 1 Max bitrate Initiate retrain
F 1 0 Max bitrate Start automodem in calling mode
F 1 1 Max bitrate Start automodem in answer mode
1 0 0 Max bitrate Initiate rate re-negotiation
F is the fast training flag bit:
In V.22 or V.22 bis modes: If F is set to 1 in a ‘start automodem in answer mode’ command the
2100Hz answer tone will not be transmitted. The F bit has no effect in other commands.
In V.32 or V.32 bis modes: If F is set to 1 a faster but less accurate echo cancellation training
algorithm is used.
The ‘Max bitrate’ field defines the maximum bitrate that will be allowed by the modem during rate
negotiations.
Max bitrate
Bit: b2 b1 b0 bps
1 1 1 14400
1 1 0 12000
1 0 1 9600
1 0 0 9600
0 1 1 7200
0 1 0 4800
0 0 1 2400
0 0 0 1200
Protocol
V.32 bis
V.32 bis
V.32 / V.32 bis (with Trellis coding)
V.32 (no Trellis coding)
V.32 bis
V.32 / V.32 bis
V.22 bis
V.22 / V.22 bis
For most applications a connection can be established by ensuring that the Tx and Rx Mode registers
have been set to QAM modem mode and that the Status Register b13 = 1 then writing a ‘Start
automodem (calling or answer mode)’ command with the Max bitrate field set to 14400bps. The CMX869
will automatically attempt to execute the entire start-up procedure as described in V.32 bis, including the
V.25 automatic answering sequence, receiver training and rate negotiation. Significant events occurring
during this process will be reported in the QAM Modem Status Register. When a data connection has
been established b3-0 of the QAM Modem Status Register will show a value of between 1000 and 1111,
indicating the negotiated bit rate.
The CMX869 will automatically respond to V.32/V.32 bis retrain and rate re-negotiation requests from the
distant modem; alternatively the ‘Initiate retrain’ and ‘Initiate rate re-negotiation’ commands can be used
to initiate such requests. In both cases the progress of the retrain or rate re-negotiation will be reported in
the QAM Modem Status Register.
© 2003 CML Microsystems Plc
27
D/869/1
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