Data Sheet

Ethernet Controller I210 —Interconnects
116
3.7.8.1.3 Auto Negotiation
The PHY supports the IEEE 802.3u auto-negotiation scheme with next page capability. Next page
exchange uses Register 7 to send information and Register 8 to receive them. Next page exchange can
only occur if both ends of the link advertise their ability to exchange next pages.
3.7.8.1.4 Parallel Detection
Parallel detection can only be used to establish 10 and 100 Mb/s links. It occurs when the PHY tries to
negotiate (transmit FLPs to its link partner), but instead of sensing FLPs from the link partner, it senses
100BASE-TX MLT3 code or 10BASE-T Normal Link Pulses (NLPs) instead. In this case, the PHY
immediately stops auto-negotiation (terminates transmission of FLPs) and immediately brings up
whatever link corresponds to what it has sensed (MLT3 or NLPs). If the PHY senses both technologies,
the parallel detection fault is detected and the PHY continues sending FLPs.
With parallel detection, it is impossible to determine the true duplex state of the link partner and the
IEEE standard requires the PHY to assume a half-duplex link. Parallel detection also does not allow
exchange of flow-control ability (PAUSE and ASM_DIR) or the master/slave relationship required by
1000BASE-T. This is why parallel detection cannot be used to establish GbE links.
3.7.8.1.5 Auto Cross-Over
Twisted pair Ethernet PHY's must be correctly configured for MDI or MDI-X operation to inter operate.
This has historically been accomplished using special patch cables, magnetics pinouts or Printed Circuit
Board (PCB) wiring. The PHY supports the automatic MDI/MDI-X configuration originally developed for
1000Base-T and standardized in IEEE 802.3u section 40. Manual (non-automatic) configuration is still
possible.
For 1000BASE-T links, pair identification is determined automatically in accordance with the standard.
For 10/100/1000 Mb/s links and during auto-negotiation, pair usage is determined by bits 4 and 5 in
PHYREG 0,21. The PHY activates an automatic cross-over detection function if enabled via bit 0 in
IPCNFG (also see bits 5 and 6 in PHYREG 0,16). When in this mode, the PHY automatically detects
which application is being used and configures itself accordingly.
The automatic MDI/MDI-X state machine facilitates switching the MDI_PLUS[0] and MDI_MINUS[0]
signals with the MDI_PLUS[1] and MDI_MINUS[1] signals, respectively, prior to the auto-negotiation
mode of operation so that FLPs can be transmitted and received in compliance with Clause 28 auto-
negotiation specifications. An algorithm that controls the switching function determines the correct
polarization of the cross-over circuit. This algorithm uses an 11-Bit Linear Feedback Shift Register
(LFSR) to create a pseudo-random sequence that each end of the link uses to determine its proposed
configuration. After making the selection to either MDI or MDI-X, the node waits for a specified amount
of time while evaluating its receive channel to determine whether the other end of the link is sending
link pulses or PHY-dependent data. If link pulses or PHY-dependent data are detected, it remains in that
configuration. If link pulses or PHY-dependent data are not detected, it increments its LFSR and makes
a decision to switch based on the value of the next bit. The state machine does not move from one
state to another while link pulses are being transmitted.