SGMII Protocol Support

Computers & Servers

Serial Gigabit Media Independent Interface

What is SGMII?

SGMII (Serial Gigabit Media Independent Interface) is a serial alternative to GMII and RGMII for Gigabit Ethernet MAC-to-PHY connections. Originally defined by Cisco, SGMII uses a single differential pair in each direction (TX+/-, RX+/-) running at 1.25 Gbps with 8b/10b encoding. SGMII drastically reduces pin count to just 4 signal pins (plus optional reference clock), making it popular in switch ICs, SoCs, and multi-port Ethernet designs where routing many parallel data lines is impractical. Engineers debugging SGMII links need to verify the serial data encoding, auto-negotiation, and link status signaling that occurs in-band within the SGMII data stream.

SGMII Quick Reference

type Serial, differential
signals TX+/-, RX+/-
max Speed 1.25 Gbps
voltage Range Differential
standard Cisco SGMII

Acute Instruments Supporting SGMII

TravelLogic Series

TravelLogic Series
LA4000 Series

LA4000 Series

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How to Analyze SGMII with Acute Instruments

1

Connect your Acute logic analyzer to the SGMII TX+/-, RX+/- differential pairs using appropriate differential probes.

2

Attach a ground lead to the target board's ground reference.

3

In the Acute software, select the SGMII protocol decoder and assign the differential signals to the correct input channels.

4

Configure the decoder for the expected line rate and encoding.

5

Capture and view decoded SGMII data showing Ethernet frame content and in-band auto-negotiation status.

Frequently Asked Questions

What sample rate is required for SGMII analysis?
SGMII operates at 1.25 Gbps serial rate. For data content decoding, this exceeds typical logic analyzer sample rates. However, Acute logic analyzers can capture lower-level aspects of SGMII such as link status signaling and in-band auto-negotiation. For full serial data capture at 1.25 Gbps, specialized high-speed analyzers or oscilloscopes are typically required.
Why is my SGMII link not establishing?
SGMII link establishment depends on in-band auto-negotiation, which exchanges link parameters (speed, duplex) using a modified Ethernet auto-negotiation mechanism within the serial stream. Common failure causes include reference clock issues, incorrect serializer/deserializer (SerDes) configuration, PCB differential pair impedance mismatch, or incompatible auto-negotiation settings between the MAC and PHY. Verify the reference clock presence and frequency, and check PHY register configuration via MDIO.
How many channels are needed for SGMII analysis?
SGMII requires 4 channels for the two differential pairs (TX+, TX-, RX+, RX-). If a reference clock is present, add 1-2 channels. For monitoring the MDIO management interface alongside SGMII, add 2 more channels for MDC and MDIO. Total: 4-8 channels depending on what signals you need to monitor.

Related Protocols

RGMII GMII

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