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
15
0
14
0
13
0
12
0
11
0
10
0
9
0
8
0
7
0
6
0
5
4
3
2
1
0
Bit:
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
F
F
F
1
0
0
1
1
0
0
1
0
1
0
0
0
0
Stop modem
Initiate retrain
Start automodem in calling mode
Start automodem in answer mode
Initiate rate re-negotiation
Max bitrate
Max bitrate
Max bitrate
Max bitrate
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
1
1
1
1
0
0
0
0
b1
1
1
0
0
1
1
0
0
b0
1
0
1
0
1
0
1
0
bps
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
14400
12000
9600
9600
7200
4800
2400
1200
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. If the rate re-negotiation is unsuccessful with the maximum bit rate set to
4800 baud or above, re-initiate the rate re-negotiation with the maximum bit rate set to 2400 baud
(V.22bis) or less.
© 2004 CML Microsystems Plc
27
D/869/4
CMLMICRO [ CML MICROCIRCUITS ]
