LAN8804 datasheet(40/91 Pages) MICROCHIP

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LAN8804

DS00003591G-page 40

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.

The MSE value is compared to the thresholds set in the DCQ SQI Table Registers to provide an SQI value between 0

(worst value) and 7 (best value) as follows:

In order to capture the SQI 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 SQI register.

In addition to the current SQI, the worst case (lowest) SQI since the last read is available in the SQI Worst Case field.

The correlation between the SQI values stored in the DCQ SQI register and an according Signal to Noise Ratio (SNR)

based on Additive White Gaussian (AWG) noise (bandwidth of 80 MHz @ 100 Mbps / 550 MHz @ 1000 Mbps) is shown

in Table 5-4 and Table 5-5. The bit error rates to be expected in the case of white noise as interference signal is shown

in the table as well for information purposes.

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.

TABLE 5-3:

MSE TO SQI MAPPING

MSE Value

SQI Value

Greater Than

Less Than or Equal To

—

SQI_TBL7.SQI_VALUE

SQI_TBL6.SQI_VALUE

SQI_TBL5.SQI_VALUE

SQI_TBL4.SQI_VALUE

SQI_TBL3.SQI_VALUE

SQI_TBL2.SQI_VALUE

SQI_TBL1.SQI_VALUE

—

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