SNLA431 January 2024 DP83TC812R-Q1 , DP83TC812S-Q1
The IEEE802.3bw standard specifies several electrical tests to maintain proper transmitter electrical specifications of 100Base-T1 PHYs. These tests can be used to confirm the components and layout of a design are meeting requirements and not affecting the signal quality. See SNLA389 for more details on performing these tests. Note the script given in SNLA389 must be written at all times during regular operation of the PHY, not just for compliance testing.
For designs with link issues or CRC errors determined to be stemming from the MDI, performing these compliance tests can give additional insight on the issue. For example, a design failing the PSD test can point to the MDI traces being very long and having increased insertion loss. A design failing the jitter test can point to cross talk from nearby switching signals. Please refer to the DP83TC812 Schematic Checklist for recommended layout rules.
Most oscilloscope vendors have software and fixtures to run the 100Base-T1 PMA compliance tests. One such option can be found here. Below is a list of PMA compliance tests, and corresponding PHY test modes required.
PMA Compliance Test | Required PHY Test Mode |
---|---|
Transmitter Output Droop | Test Mode 1 |
Transmitter Clock Frequency | Test Mode 2 |
Transmitter Timing Jitter | Test Mode 2 |
Transmitter Distortion | Test Mode 4 |
Peak Differential Output | Test Mode 5 |
Transmitter Power Spectral Density (PSD) | Test Mode 5 |
MDI Return Loss | n/a |
MDI Mode Conversion | n/a |