lxt9785 Intel Corporation, lxt9785 Datasheet - Page 129

• Manufacturer Part Number: lxt9785
• Description: Advanced 8-port 10/100 Mbps Phy Transceivers
• Manufacturer: Intel Corporation

4.6.1.5
4.6.1.6
Datasheet
Document Number: 249241
Revision Number: 007
Revision Date: August 28, 2003
Figure 14. Intel
Parallel Detection
In parallel with auto-negotiation, the LXT9785/LXT9785E also monitors for 10 Mbps Normal
Link Pulses (NLP) or 100 Mbps Idle symbols. If either symbol is detected, the device
automatically reverts to the corresponding operating speed in half-duplex mode. Parallel detection
allows the LXT9785/LXT9785E to communicate with devices that do not support auto-
negotiation.
When parallel detection resolves a link, the link must be established in half-duplex mode.
According to IEEE standards, the forced link partner cannot be configured to full-duplex. If the
auto-negotiation link partner does not advertise half-duplex capability at the speed of the forced
link partner, link is not established. The IEEE Standard prevents forced full-duplex-to-half-duplex
link connections.
Reliable Link Establishment While Auto MDI/MDIX is Enabled in Forced
Speed Mode
With auto MDI/MDIX hardware enabled, end users experience reliable link establishment under all
settings of auto MDI/MDIX and speed between the LXT9785/LXT9785E and its link partners. As
stated in the IEEE clauses 40.4.5.1 (Auto MDI/MDIX) and 28.3.2 (Parallel Detect), when ports are
forced to 10 Mbps or 100 Mbps and auto MDI/MDIX is enabled, and the port is connected to a
partner with auto-negotiation enabled, an undefined condition exists between the IEEE auto MDIX
and Parallel Detect specifications. Link may not occur according to the IEEE specification.
During this undefined condition, when the LXT9785/LXT9785E is set to 10 Mbps or 100 Mbps
and auto MDI/MDIX is enabled, the LXT9785/LXT9785E and the link partner auto-negotiation
processes are expected to be skewed enough to establish link in all but the rarest cases. Auto MDI/
MDIX is configured through hardware and software. If auto MDI/MDIX operation is desired in
forced modes, disabling auto MDI/MDIX using the software programming can aid link
establishment.
®
LXT9785/LXT9785E Auto-Negotiation Operation
Auto-Negotiation
Go To Forced
LXT9785 and LXT9785E Advanced 8-Port 10/100 Mbps PHY Transceivers
Disable
Settings
Done
0.12 = 0
Power-Up, Reset,
Link Failure
Check Value
Attempt Auto-
Start
0.12
Negotiation
0.12 = 1
YES
Listen for 100TX
Auto-Neg/Parallel Detection
Idle Symbols
Link Set?
Enable
NO
Listen for 10T
Link Pulses
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