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April, 2002
L84225 Quad 100BaseTX/FX/10BaseT Phys. Layer Device - Technical Manual
Copyright 1999-2002 by LSI Logic Corporation. All rights reserved.
2.18 10/100 MBPS Selection
2.18.1 General
The device can be forced into either the 100 or 10 Mbps mode, or the
device can detect 100 or 10 Mbps capability from a remote device and
automatically place itself in the correct mode.
The device can be forced into either the 100 or 10 Mbps mode by either
setting the speed select bit in the MI serial port Control register or by
setting the SPEED pin with AutoNegotiation disabled. Both the speed
select bit and SPEED pin need to be set to the same speed (10 or 100)
for the device to be properly configured. The speed select bit and SPEED
pin are ignored if AutoNegotiation is enabled.
The device can automatically configure itself for 100 or 10 Mbps mode
by using the AutoNegotiation algorithm to advertise and detect 100 and
10 Mbps capabilities to and from a remote device. Refer to
Section 2.14,
“Link Integrity and AutoNegotiation,” page 40
, for more details on
AutoNegotiation.
2.18.2 10/100 MBPS Indication
The device speed (100/10 Mbps) can be monitored through the speed
bit in the MI serial port Channel Status Output register.
The device speed can also be programmed to appear on the LED0 pin,
by appropriately setting the LED definition bits in the MI serial port Global
Configuration register.
Section 2.23, “LED Drivers,” page 48
, describes
the programmable LED definition bit settings. When the LED0 pin is
programmed to be a speed detect output, the pin is asserted low when
the device is configured for 100 Mbps operation.
2.19 Loopback
2.19.1 Internal CRS Loopback
TXEN is internally looped back onto CRS during every transmit packet.
This internal CRS loopback is disabled during collision, in Full Duplex
mode, in Link Fail State, and in RMII mode. In 10 Mbps mode, internal
CRS loopback is also disabled when jabber is detected.