Data Sheet

Design Considerations—Ethernet Controller I210
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8. Incorrect differential trace impedances. It is important to have ~100  impedance between the two
traces within a differential pair. This becomes even more important as the differential traces
become longer. To calculate differential impedance, many impedance calculators only multiply the
single-ended impedance by two. This does not take into account edge-to-edge capacitive coupling
between the two traces. When the two traces within a differential pair are kept close to each other,
the edge coupling can lower the effective differential impedance by 5  to 20 . Short traces have
fewer problems if the differential impedance is slightly off target.
12.6 SMBus and NC-SI
SMBus and NC-SI are optional interfaces for pass-through and/or configuration traffic between the MC
and I210. See Section 3.2.1 and Section 3.2.2 for more details.
This section describes the hardware implementation requirements necessary to meet the NC-SI
physical layer standard. Board-level design requirements are included for connecting I210 Ethernet
solution to an external MC. The layout and connectivity requirements are addressed in low-level detail.
This section, in conjunction with the Network Controller Sideband Interface (NC-SI) Specification
Version 1.0 RMII Specification, also provides the complete board-level requirements for the NC-SI
solution.
The I210’s on-board System Management Bus (SMBus) port enables network manageability
implementations required for remote control and alerting via the LAN. With SMBus, management
packets can be routed to or from an MC. Enhanced pass-through capabilities also enable system remote
control over standardized interfaces. Also included is a new manageability interface, NC-SI that
supports the DMTF preOS sideband protocol. An internal management interface called MDIO enables
the MAC (and software) to monitor and control the PHY.
12.6.1 NC-SI Electrical Interface Requirements
12.6.1.1 External MC
The external MC is required to meet the latest NC-SI specification as it relates to the RMII electrical
interface.
12.6.1.2 NC-SI Reference Schematics
Figure 12-17 shows the single-drop application connectivity requirements. Figure 12-18 shows the
multi-drop application connectivity requirements Figure 11-16 shows the hardware arbitration
connectivity requirements. Refer to the latest NC-SI specification for any additional connectivity
requirements.