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How Do I Start Using the Beagle I2C/SPI Protocol Analyzer to Monitor the MDIO Bus?
Rena Ayeras

Question from the Customer:

This is my first project – can you help me get started? I am using the Beagle I2C/SPI Protocol Analyzer to monitor the MDIO bus. Which pins I should connect it to MDC/MDIO?

Response from Technical Support:

Thanks for your question! Here is the information to help you get started.

How the Beagle I2C/SPI Analyzer Works with MDIO

The Beagle I2C/SPI analyzer non-intrusively monitors the Management Data Input/Output (MDIO) up to 2.5 MHz at signal level 3.3V. To monitor an MDIO bus that has a different voltage level, you can use Total Phase Level Shifter Board. Here are the pin numbers of the signals you asked about.

  • MDIO signal, pin 8, is the bidirectional management data input/output. MIDO is used to transfer data between the Station Management Entity (STA) and the MDIO Manageable Devices (MMD)..
  • MDC signal, pin 7, is the management data clock. This is a control line that is driven by the STA, and synchronizes the flow of the data on the MDIO line.

The Beagle I2C/SPI analyzer monitors MDIO for both clause 22 and clause 45.

MDIO Clause 22 and Clause 45

Clause 22 and clause 45 are parts of the IEEE 802.3 specification.

Clause 22 defines the MDIO communication basic frame format, as shown below.

MDIO Clause 22 frame

MDIO clause 45 communication frame format table

Clause 45 supports low voltage devices down to 1.2V, and extends the frame format, providing access to more devices and registers.

MDIO clause 45 communication frame format

MDIO Clause 45 table

For more information, please refer to the knowledge base article MDIO Background. We also recommend Use The MDIO Bus To Interrogate Complex Devices, published by Electronic Design Magazine

How to Capture MDIO Signals

To accurately capture MDIO signals, the sampling rate must be set properly. The minimum requirement for the sampling rate is twice the bus bit rate. For details, please refer to the following:

We hope this answers your question. Additional resources that you may find helpful include the following:

Looking for more information? You can contact us and request a demo that applies to your application, as well as ask about Total Phase products.

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