LXT972 Level One, LXT972 Datasheet - Page 17

• Manufacturer Part Number: LXT972
• Description: 3.3V Dual-Speed Fast Ethernet Transceiver Datasheet
• Manufacturer: Level One

Establishing Link
See
Auto-Negotiation
If not configured for forced operation, the LXT972
attempts to auto-negotiate with its link partner by sending
Fast Link Pulse (FLP) bursts. Each burst consists of up to
33 link pulses spaced 62.5 s apart. Odd link pulses (clock
pulses) are always present. Even link pulses (data pulses)
may be present or absent to indicate a “1” or a “0”. Each
FLP burst exchanges 16 bits of data, which are referred to
as a “link code word”. All devices that support auto-
negotiation must implement the “Base Page” defined by
IEEE 802.3 (registers 4 and 5). LXT972 also supports the
optional “Next Page” function as described in
and 45
Figure 7: Link Establishment Overview
Base Page Exchange
Figure 7
By exchanging Base Pages, the LXT972 and its link
partner communicate their capabilities to each other.
Both sides must receive at least three identical base
pages for negotiation to continue. Each side identifies
the highest common capabilities that both sides
support and configures itself accordingly.
(registers 7 and 8).
Auto-Negotiation
for an overview of link establishment.
Go To Forced
Disable
Settings
Done
0.12 = 0
Power-Up, Reset,
or Link Failure
C h e c k V a l u e
Tables 44
Attempt Auto-
Start
0.12
Negotiation
0.12 = 1
Parallel Detection
For the parallel detection feature of auto-negotiation, the
LXT972 also monitors for 10BASE-T Normal Link Pulses
(NLP) and 100BASE-TX Idle symbols.
detected, the device automatically reverts to the
corresponding operating mode. Parallel detection allows
the LXT972 to communicate with devices that do not
support auto-negotiation.
YES
Next Page Exchange
Controlling Auto-Negotiation
Additional information, above that required by base
page exchange, is also sent via “Next Pages’. The
LXT972 fully supports the IEEE 802.3ab method of
negotiation via Next Page exchange.
When auto-negotiation is controlled by software, the
following steps are recommended:
• After power-up, power-down, or reset, the
• Set the auto-negotiation advertisement register
• Enable auto-negotiation (set MDIO bit 0.12 = 1).
Listen for 100TX
power-down recovery time, as specified in
Table 34 on page
proceeding.
bits.
Auto-Neg/Parallel Detection
Idle Symbols
Link Up?
LXT972 Functional Description
Enable
47, must be exhausted before
N O
Listen for 10T
Link Pulses
If either is
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