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DP83847
2.0 Configuration
This section includes information on the various configura-
tion options available with the DP83847. The configuration
options described below include:
— Auto-Negotiation
— PHY Address and LEDs
— Half Duplex vs. Full Duplex
— Isolate mode
— Loopback mode
—BIST
2.1 Auto-Negotiation
The Auto-Negotiation function provides a mechanism for
exchanging configuration information between two ends of
a link segment and automatically selecting the highest per-
formance mode of operation supported by both devices.
Fast Link Pulse (FLP) Bursts provide the signalling used to
communicate Auto-Negotiation abilities between two
devices at each end of a link segment. For further detail
regarding Auto-Negotiation, refer to Clause 28 of the IEEE
802.3u specification. The DP83847 supports four different
Ethernet protocols (10 Mb/s Half Duplex, 10 Mb/s Full
Duplex, 100 Mb/s Half Duplex, and 100 Mb/s Full Duplex),
so the inclusion of Auto-Negotiation ensures that the high-
est performance protocol will be selected based on the
advertised ability of the Link Partner. The Auto-Negotiation
function within the DP83847 can be controlled either by
internal register access or by the use of the AN_EN, AN1
and AN0 pins.
2.1.1 Auto-Negotiation Pin Control
The state of AN_EN, AN0 and AN1 determines whether the
DP83847 is forced into a specific mode or Auto-Negotiation
will advertise a specific ability (or set of abilities) as given in
Table 1. These pins allow configuration options to be
selected without requiring internal register access.
The state of AN_EN, AN0 and AN1, upon power-up/reset,
determines the state of bits [8:5] of the ANAR register.
The Auto-Negotiation function selected at power-up or
reset can be changed at any time by writing to the Basic
Mode Control Register (BMCR) at address 00h.
2.1.2 Auto-Negotiation Register Control
When Auto-Negotiation is enabled, the DP83847 transmits
the abilities programmed into the Auto-Negotiation Adver-
tisement register (ANAR) at address 04h via FLP Bursts.
Any combination of 10 Mb/s, 100 Mb/s, Half-Duplex, and
Full Duplex modes may be selected.
The BMCR provides software with a mechanism to control
the operation of the DP83847. The AN0 and AN1 pins do
not affect the contents of the BMCR and cannot be used by
software to obtain status of the mode selected. Bits 1 & 2 of
the PHYSTS register are only valid if Auto-Negotiation is
disabled or after Auto-Negotiation is complete. The Auto-
Negotiation protocol compares the contents of the
ANLPAR and ANAR registers and uses the results to auto-
matically configure to the highest performance protocol
between the local and far-end port. The results of Auto-
Negotiation (Auto-Neg Complete, Duplex Status and
Speed) may be accessed in the PHYSTS register.
Auto-Negotiation Priority Resolution:
— (1) 100BASE-TX Full Duplex (Highest Priority)
— (2) 100BASE-TX Half Duplex
— (3) 10BASE-T Full Duplex
— (4) 10BASE-T Half Duplex (Lowest Priority)
The Basic Mode Control Register (BMCR) at address 00h
provides control for enabling, disabling, and restarting the
Auto-Negotiation process. When Auto-Negotiation is dis-
abled the Speed Selection bit in the BMCR controls switch-
ing between 10 Mb/s or 100 Mb/s operation, and the
Duplex Mode bit controls switching between full duplex
operation and half duplex operation. The Speed Selection
and Duplex Mode bits have no effect on the mode of oper-
ation when the Auto-Negotiation Enable bit is set.
The Basic Mode Status Register (BMSR) indicates the set
of available abilities for technology types, Auto-Negotiation
ability, and Extended Register Capability. These bits are
permanently set to indicate the full functionality of the
DP83847 (only the 100BASE-T4 bit is not set since the
DP83847 does not support that function).
Table 1. Auto-Negotiation Modes
AN_EN AN1 AN0 Forced Mode
0 0 0 10BASE-T, Half-Duplex
0 0 1 10BASE-T, Full-Duplex
0 1 0 100BASE-TX, Half-Duplex
0 1 1 100BASE-TX, Full-Duplex
AN_EN AN1 AN0 Advertised Mode
1 0 0 10BASE-T, Half/Full-Duplex
1 0 1 100BASE-TX, Half/Full-Duplex
1 1 0 10BASE-T Half-Duplex
100BASE-TX, Half-Duplex
1 1 1 10BASE-T, Half/Full-Duplex
100BASE-TX, Half/Full-Duplex
