Filter
Top Products
130 10/100 Mbps Ethernet Controller Family Open Source Software Developer Manual
Physical Layer Interface
7.4 Auto-Negotiation Functionality
The PHY units of the 8255x devices (excluding the 82557) all support auto-negotiation (N-Way).
Auto-negotiation is an automatic configuration scheme designed to manage interoperability in
heterogeneous LAN environments. It allows two stations with “N” different modes of
communication to establish one common mode of operation. Upon power-up, auto-negotiation
establishes a link using one or more devices capable of auto-negotiating. An hub that supports
auto-negotiation can detect and automatically configure its ports to take maximum advantage of
common modes of operation without user intervention or prior knowledge by either station. The
possible common modes of operation are: 100BASE-TX, 100BASE-TX full duplex, 10BASE-T,
and 10BASE-T full duplex.
7.4.1 Description
Auto-Negotiation selects the fastest operating mode (in other words, the highest common
technology denominator) available to hardware at both ends of the cable. A PHY’s capability is
encoded by bursts of link pulses called Fast Link Pulses (FLPs). Connection is established by FLP
exchange and handshake during initialization time. Once the link is established by this handshake,
the native link pulse scheme resumes (for example, 10BASE-T or 100BASE-TX). If only one end
of the twisted pair is auto-negotiation capable, then the FLP exchange fails and another scheme
called parallel detection is used to determine the link settings. A PHY reset, or management
renegotiate command (through the MDI interface), restarts the auto-negotiation process. To enable
auto-negotiation, bit 12 of the MDI Control Register must be set. If the PHY cannot perform auto-
negotiation, this bit is set to 0.
Since only one technology can be used at a time (after every renegotiate command), a prioritization
scheme must be used to ensure that the highest common denominator ability is chosen. Table 64
lists the technology ability field bit assignments. Each bit in this table is set according to the PHY
capability. Table 65 lists the priority of each of the technologies.
Table 63. LED Switch Control
Bits
2:0
ACTLED# Pin LILED# Pin
000 Activity Link
001 Speed Collision
010 Speed Link
011 Activity Collision
100 Off Off
101 Off On
110 On Off
111 On On