RCVDL56DPFL/SP, RCV56DPFL/SP, and RCV336DPFL/SP Designer’s Guide
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When the MDP determines, from the bandwidth, the maximum supportable symbol rate, the MDP will enable all symbol
rates below that maximum value. For example, if the line probe indicates that the bandwidth is adequate to support 3000
baud, then 2800 and 2400 baud will also be supported. This selection of symbol rates is, however, dependent upon the
contents of the BMR. Again, for the same example, if a host does not want to support 2800 baud, the host must reset bit 2
of the BMR. If both modems do not agree during probing, e.g., the originate modem chooses 3000 baud and the answer
modem chooses 2800 baud, then the highest common rate will be 2400 baud. In the event there is no common rate, the
modems will default to 2400 baud.
Figure 4-9 shows the symbol rate negotiation process. The final symbol rate chosen may be read from address 2E3h after
the negotiation is complete. A value of 10h, for example, would indicate a symbol rate of 3200 baud.
1026F4-9 SRNP
Max Rate from Line Probe
Baud Mask Register
Symbol Rates Suggested
Common Symbol Rate
Max Rate from Line Probe
Baud Mask Register
Symbol Rates Suggested
Common Symbol Rate
ORIGINATE
ANSWER
Figure 4-9. V.34 Symbol Rate Negotiation Process
Function 62:
V.34 Pre-Emphasis Filter Number
Acc. Method: 4
Addr.: B44h
Function 63:
V.34 Pre-Emphasis Filter Override Number
Acc. Method: 1
Addr.: 0E6h
V.34 Emphasis Disable
Acc. Method: 1
Addr.: 100h:1
There are 11 pre-emphasis filters defined, each matching the templates defined in ITU-T V.34.
The Pre-emphasis filter selected can be read from the V.34 Pre-Emphasis Filter Number (address B44h).
The Pre-emphasis negotiation can be ignored by setting bit 100h:1, Pre-emphasis Disable (PREDIS). This bit does not stop
the measurement or the transmission of the suggested pre-emphasis filter, but rather causes the receiver to ignore the
suggestion.
Pre-emphasis can also be controlled by using the CEQ bit in the MDP interface memory. If this bit is reset, any selected pre-
emphasis or transmit compromise filter will be ignored. In this way, the host can control pre-emphasis by setting/resetting
CEQ. However, if the host wishes to use a custom compromise filter, then by using the PREDIS bit, the suggested filter will
be ignored and the host's custom defined compromise filter will be used.
The procedure to manually select one of the pre-emphasis filters is:
1. Set the PREDIS bit (100h:1) to override negotiation.
2. Load the Pre-Emphasis Filter Over-Ride Number (address 0E6h) with the Pre-emphasis Filter Suggestion Number from
the table above.
3. Ensure that CEQ is on.
Function 64:
V.34 Transmit Level Deviation Disable
Acc. Method: 1
Addr.: 100h:3
During line probing, the MDP measures the receive level of the line signal. If that receive level is high enough, the MDP
suggests that the remote modem reduce its own transmit level in order to improve signal-dependent noise performance.
The transmit level power drop does not use receive level alone. Decision is also based on noise and harmonic distortion
criteria.
To force the MDP to ignore the suggested transmit level reduction, set the Transmit Level Deviation Disable (TLDDIS) bit
(100h:3) to a 1.
Содержание RC336DPFL
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