LAN8804D datasheet(39/89 Pages) MICROCHIP

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LAN8804D

DS00003591K-page 39

5.11.3

OPEN ALLIANCE TC1/TC12 DCQ MEAN SQUARE ERROR

This section defines the implementation of section 6.1.1 of the TC1 and TC12 specifications. The PHY can provide

detailed information of the dynamic signal quality by means of an MSE value. This mode is enabled by setting the

sqi_enable bit in the DCQ Configuration register.

With this method, the slicer error is converted into a squared value and then filtered by a programmable low pass filter.

This is similar to taking the average of absolute slicer error over a long moving time window.

For each data sample, the difference between the absolute slicer error (scaled by x2 (before squaring) for 1000BASE-

T) and the current filtered value is added back into the current filtered value.

The sqi_squ_mode_en bit in the DCQ Configuration register must be set to choose square mode.

The sqi_kp field in the DCQ Configuration register sets the weighting of the add back as a divide by 2^sqi_kp, effectively

setting the filter bandwidth. As the sqi_kp value is increased, the weighing is decreased, and the mean slicer error value

takes a longer time to settle to a stable value. Also, as the sqi_kp value is increased, there will be less variation in the

mean slicer error value reported.

The scale611 field in the DCQ Configuration register is used to set a divide by factor (divide by 2^scale611) such that the

Mean Squared Error (MSE) value is linearly scaled to the range of 0 to 511. If the divide by factor is too small, the MSE

value is capped at a maximum of 511.

The filtered error value is saved every 1.0 ms (125,000 symbols).

In order to capture the MSE value, the DCQ Read Capture bit in the DCQ Configuration register needs to be written as

a high with the desired cable pair specified in the DCQ Channel Number field of the same register. The DCQ Read Cap-

ture= bit will immediately self-clear and the result will be available in the DCQ Mean Square Error register.

In addition to the current MSE value the worst case MSE value since the last read of DCQ Mean Square Error register

is stored in DCQ Mean Square Error Worst Case register.

5.11.4

OPEN ALLIANCE TC1/TC12 DCQ SIGNAL QUALITY INDEX

This section defines the implementation of section 6.1.2 of the TC1 and TC12 specifications. This mode builds upon the

OPEN Alliance TC1/TC12 DCQ Mean Square Error method by mapping the MSE value onto a simple quality index. This

mode is enabled by setting the sqi_enable bit, in the DCQ Configuration register.

Note:

All registers references in this section are in Extended Page 1.

Note:

All registers references in this section are in Extended Page 1.

Note:

As in the OPEN Alliance TC1/TC12 DCQ Mean Square Error method, the sqi_squ_mode_en bit in the DCQ

Configuration register must be set to choose square mode.

Note:

As above in the OPEN Alliance TC1/TC12 DCQ Mean Square Error method, the scale611 field in the DCQ

Configuration register is used to set the divide by factor (divide by 2^scale611) such that the MSE value is

linearly scaled to the range of 0 to 511.

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