
Draft 6/5/00
Full/Half Duplex Mode
2-37
Copyright 1999 by LSI Logic Corporation. All rights reserved.
2.6 Full/Half Duplex Mode
Half-Duplex mode is the CSMA/CD operation defined in IEEE 802.3. It
allows transmission or reception, but not both at the same time. Full-
Duplex operation is a mode that allows simultaneous transmission and
reception. Full duplex in the 10 Mbits/s mode is identical to operation in
the 100 Mbits/s mode.
The device can be forced into either the Full- or Half-Duplex mode, or
the device can use AutoNegotiation to autoselect Full/Half-Duplex
operation. When a channel is placed in Full Duplex mode:
The collision function is disabled, and
TX_EN to CRS loopback is disabled
2.6.1 Forcing Full/Half Duplex Operation
To independently force a channel into either the Full- or Half-Duplex
mode, set the Duplex Mode Select (DPLX) bit in the MI serial port
Control register, assuming that AutoNegotiation is not enabled with the
ANEG_EN bit in the MI serial port Control register.
The device automatically configures itself for Full- or Half-Duplex mode.
To do this, the device uses the AutoNegotiation algorithm to advertise
and detect Full and Half Duplex capabilities to and from a remote device.
To enable AutoNegotiation, set the AutoNegotiation Enable (ANEG_EN)
bit in the MI serial port Control register.
To select the advertised Full/Half Duplex capability, appropriately set the
bits in the MI serial port AutoNegotiation Advertisement register.
AutoNegotiation functionality is described in more detail in
Section
2.3.10, “Link Integrity and AutoNegotiation”
.
2.6.2 Full/Half Duplex Indication
Full Duplex detection can be monitored through the DPLX_DET bit in the
MI serial port Status Output register, or it can also be programmed to
appear on the PLEDn1 pin.
In the MI serial port Configuration register, set the LED function select
bits (LED_DEF[1:0]) so that the full duplex condition activity is indicated