The ALCD will need to be calibrated to each cable type and application by measuring the ALCD register information at five regular intervals up to the maximum cable reach the application requires. The calibration can be done in a designer's lab during product evaluation. A good cable will not deviate much in its characteristics from the test cable used in calibration to those deployed in the field, allowing calibration to be performed once for a PHY-cable pair. To perform the calibration and estimate the cable reach of a link, follow the following procedure.

1. The maximum cable length expected to be used in the field with DP83TD510E Ethernet PHY is referred to as maximum operating length with the Ethernet PHY. For example, if 900 m is expected to be the longest cable length which will be used in the field, then 900 m is called as the maximum operating length. ALCD will have reference data for the maximum operating length with some margin for degradation in the cable performance over time. The margin can be fixed (say 10%) or can be derived from the performance with the higher cable length. For the example we can assume a 10% margin and generate reference data for approximately 1 km. It will be referred to as ALCD range.
2. The ALCD calibration is done in five segments of ALCD cable range. It is recommended that these segments are equal or nearly equal in length. For example, we can use either of the following cable lengths for calibrating ALCD or any other set close to these values for ALCD range of 900m. Do keep in mind that the longest cable length for calibration needs to be greater than actual used cable.

   Set 1: {0m, 200m, 400m, 600m, 800m, 1km}

3. An ALCD metric is calculated by the PHY for each segment of the ALCD cable range. It is internally generated by the silicon and is displayed in register 0x0A9D after the link up is achieved. Follow the procedure below to read the correct value of the ALCD metric at each segment length.
   1. Program with a desired script if necessary, and let the devices link up.
   2. Wait for 3ms after the link up is achieved and read register 0x0A9D for the ALCD metric.
   3. Ignore the LSB hexadecimal digit, and store the 3 MSB hexadecimal digits of the metric.
   4. Repeat steps a. through c. for all cable lengths in the calibration set to obtain a calibration pair for 1 V mode and 2.4 V mode.
4. Once the ALCD reference metric is recorded for each cable length, these values can be stored in the DP83TD510E registers to estimate the length of the cable over the lifetime of the application. Six pairs of <cable, metric> are required to be generated following the procedure described above. This information needs to be stored in registers as per Table 4-1 and needs to be part of initial link up script.

Figure 4-1 Example Reading For Calibration

Procedure to generate ALCD metric:

//For each output operating mode utilized in an application, record ALCD <cable, metric pair>
 
1.0 Vpp operating ALCD metrics
//For each cable length segment in ALCD range, record the ALCD metric
begin
0001 //check that link is established in 0x0001[2]
0A9D //read register 0x0A9D and record bits [15:4] for 
end
 
2.4 Vpp operating ALCD metrics
//For each cable length segment in ALCD range, record the ALCD metric
begin
0001 //check that link is established in 0x0001[2]
0A9D //read register 0x0A9D and record bits [15:4] for 
end

Set ALCD calibration registers during initialization routine:

begin
//Set ALCD cable length segments
08E9 0000 //Cable length 1 is 0 meters
08EA 0019 //Cable length 2 is 200 meters ([200 meters / 8] -> converted to hex)
08EB 0032 //Cable length 3 is 400 meters ([400 meters / 8] -> converted to hex)
08EC 004B //Cable length 4 is 600 meters ([600 meters / 8] -> converted to hex)
08ED 0064 //Cable length 5 is 800 meters ([800 meters / 8] -> converted to hex)
08EE 007D //Cable length 6 is 1000 meters([1000 meters / 8] -> converted to hex)
 
//Set 1.0 Vpp ALCD metrics
0898 0046 //ALCD metric for 0 meters is 046
0899 0067 //ALCD metric for 200 meters is 067
089A 0088 //ALCD metric for 400 meters is 088
089B 0137 //ALCD metric for 600 meters is 137
089C 0178 //ALCD metric for 800 meters is 178
089D 0263 //ALCD metric for 1000 meters is 263 
 
//Set 2.4 Vpp ALCD metrics
088D 0078 //ALCD metric for 0 meters is 078
088E 0096 //ALCD metric for 200 meters is 096
088F 0120 //ALCD metric for 400 meters is 120
0890 0174 //ALCD metric for 600 meters is 174
0891 0201 //ALCD metric for 800 meters is 201
0892 0310 //ALCD metric for 1000 meters is 310
end