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DP83848I
2.0 Configuration
This section includes information on the various configura-
tion options available with the DP83848I. The configuration
o
ptions 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.
Fa
st 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 DP83848I 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
a
dvertised ability of the Link Partner. The Auto-Negotiation
function within the DP83848I 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
D
P83848I is forced into a specific mode or Auto-Negotia-
tion will advertise a specific ability (or set of abilities) as
g
iven 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,
d
etermines the state of bits [8:5] of the ANAR register.
The Auto-Negotiation function selected at power-up or
r
eset can be changed at any time by writing to the Basic
Mode Control Register (BMCR) at address 0x00h.
2.1.2 Auto-Negotiation Register Control
When Auto-Negotiation is enabled, the DP83848I transmits
t
he abilities programmed into the Auto-Negotiation Adver-
tisement register (ANAR) at address 04h via FLP Bursts.
An
y combination of 10 Mb/s, 100 Mb/s, Half-Duplex, and
Full Duplex modes may be selected.
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
s
witching 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 Link Speed can be examined through the PHY Status
R
egister (PHYSTS) at address 10h after a Link is
achieved.
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
DP83848I (only the 100BASE-T4 bit is not set since the
DP83848I does not support that function).
The BMSR also provides status on:
— Whether or not Auto-Negotiation is complete
— Whether or not the Link Partner is advertising that a re-
mote fault has occurred
— Whether or not valid link has been established
— Support for Management Frame Preamble suppression
The Auto-Negotiation Advertisement Register (ANAR)
i
ndicates the Auto-Negotiation abilities to be advertised by
the DP83848I. All available abilities are transmitted by
default, but any ability can be suppressed by writing to the
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