What are the register Access methods Clause 22 and Clause 45? | NEXTY Electronics, an electronic components and semiconductor trading company

By Access a register, you can read or update its value.
In the previous column, we explained that MDIO is defined in Clause 22 and Clause 45 of the automotive Ethernet standard (IEEE802.3). In this column, we will explain the details of Clause 22 and Clause 45 and the differences between them.

Operating principle

Register Access

Various settings are made using two serial buses, MDIO and MDC. By Access the registers, you can check and change the status of each setting, such as auto-negotiation, MACsec, TC10, and SQI (communication quality).

Please see the links below for an explanation of each function.

Register Address

Each register bit can store information of 0 or 1. The stored information can be used to set functions and check status.

Clause 22

Clause 22 will be explained as an example from the previous column, and only 5V POWER SUPPLIES voltage is supported.

Clause 45

The main difference with Clause 22 is the method of register Access. The address FRAMES is sent in the first FRAMES, and the read/write operation is specified in the second FRAMES. This allows Access to 65,536 addresses. OTHERS, POWER SUPPLIES voltage of 1.2V is supported. Clause 45 is also upwardly compatible with Clause 22, allowing for interoperability.

MDIO electrical interface

The electrical interface is different: Clause 22 devices have a VDD of 5V, while Clause 45 devices have a VDD of 1.2V.
When connecting a Clause 22 device to a Clause 45 device, a protocol-compatible voltage conversion device is required, except for Clause 45 devices that have a Clause 22 register, which do not require a conversion device.
The conversion device must drive the MDIO and MDC lines of the Clause22 and Clause45 devices in the same state, and must recognize the PHY address of the Clause22 device.
If a Clause 45 device drives FRAMES with ST=00, the Clause 22 device is ignored.

STA: Station Management Entity
MMD: MDIO Management Device
PU: Pull-Up Register

Summary

This article explained the details of and differences between Clause 22 and Clause 45. Although there are differences between Clause 22 and Clause 45 as standards, using them allows you to set functions and check their status.