RCVDL56DPFL/SP, RCV56DPFL/SP, and RCV336DPFL/SP Designer’s Guide
4-28
1119
Function 65-67: Not Applicable
Function 68:
EQM Above Threshold
Acc. Method: 1
Addr.: 133h
When the high byte of the EQM reading (address 20Dh) goes above the EQM Above Threshold, the MDP will assert the
EQMAT bit (0Bh:1). The host can set up a NEWS interrupt to monitor changes to this bit (see EQMAT in Function 17 ). The
default value of EQM Above Threshold is 30h and is written at POR and is unaffected by NEWC. The MDP does NOT reset
the EQMAT bit; the host must reset the EQMAT bit.
Function 69:
ARA-in RAM Enable
Acc. Method: 1
Addr.: 3A5h:4
EQM Scale Factor (Gain)
Acc. Method: 3
Addr.: A29h
The automatic rate adaptation (ARA) algorithm adjusts the data rate based on the level of EQM. The ARA is recommended
with the initial train and retrain only. Rate-renegotiation should be performed with ARA off, allowing the host to decide the
optimal data rate based on EQM readings. ARA is enabled by setting the EARC bit (15h:0), which defaults off.
Upon initial train and retrain, the EQM is checked during the training, just before the rate negotiation. The 4-point EQM is
compared against a table of values representing the necessary levels to achieve the corresponding V.34/V.32 bis data rates
with an EQM of around 2000h. Once the maximum achievable rate is determined, the CONF register is changed to reflect
the estimate, and is then used to suggest a data rate in the following negotiations.
Modifying the ARA Thresholds in RAM (V.34 Mode only)
The ‘ARA-in-RAM’ function is enabled by setting bit 3A5h:4 (8-bit access).
Sixteen RAM locations are allocated for the ARA-in-RAM thresholds. These occupy locations 3B0h to 3BFh.
The Search table used for determining the best data rate for a given EQM is uniquely organized. The search through the
table starts at the low address first, which represents the lowest data rate*, and progresses through to the higher data rates
as the measured EQM value during training decreases. The final measured EQM is compared to the ARA RAM table. The
EQM value must be greater than the threshold value in RAM for the corresponding data rate to be selected. For example, in
the table below, if the final measured EQM were between 0028 and 0090, the data rate of 26.4k would be selected. If the
EQM value were less than 0028, the data rate of 28.8k would be selected. As another example, to allow more aggressive
28.8k connections, the threshold under the 26.4k rate (0028) should be increased. This would require the measured EQM to
be slightly worse before falling back to 26.4k.
At the low data rates only the most significant byte of EQM is used in the threshold testing. However, as the thresholds get
smaller for the higher data rates, it is necessary to use the least significant byte of EQM for the required resolution. When
this transition occurs, the table of thresholds must contain a 0, followed by the appropriate low byte threshold value. The last
location to be searched must contain a 0 to stop further searches.
* Normally for symbol rates above 2400 baud, the starting point is at address 3B1h and the initial data rate is 4800 bps. For
the case of 2400 baud, the starting point is at 3B0h and the initial data rate is 2400 bps.
The following table of default thresholds against data rates is used in the ARA-in-RAM function.
Data Rate
(kbps)
2.4
4.8
7.2
9.6
12.0
14.4
16.8
19.2
21.6
24.0
26.4
28.8
31.2
33.6
Threshold
(Hex)
2000
1A00
1200
0C00
0A00
0900
0500
0300
0200
0090
0028
0010
0004
0001
Содержание RC336DPFL
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