Draft 6/5/00
2-46
Functional Description
Copyright 2000 by LSI Logic Corporation. All rights reserved.
2.7 10/100 Mbits/s Selection
The device can be forced into either the 10 or 100 Mbits/s mode, or it
can use AutoNegotiation to autoselect 10 or 100 Mbits/s operation.
2.7.1 Forcing 10/100 Mbits/s Operation
To independently force each channel into either the 10 Mbits/s or 100
Mbits/s mode:
Clear the ANEG_EN bit in the MI serial port Control register, and
Appropriately set the Speed Select (SPEED) bit in the MI serial port
Control register.
Alternatively, if the ANEG pin is LOW, the SPEED pin controls the speed.
Asserting the SPEED pin HIGH forces 100 Mbits/s operation and
deasserting it LOW forces 10 Mbits/s operation.
2.7.2 Autoselecting 10/100 Mbits/s Operation
The device can automatically configure itself for 10 or 100 Mbits/s mode.
To do this, it uses the AutoNegotiation algorithm to advertise and detect
10 and 100 Mbits/s capabilities to and from a remote device. Setting the
AutoNegotiation Enable (ANEG_EN) bit in the MI serial port Control
register enables AutoNegotiation. Appropriately setting the bits in the MI
serial port AutoNegotiation Advertisement register selects the advertised
speed capability. AutoNegotiation functionality is described in more detail
in
Section 2.2.11, “Link Integrity and AutoNegotiation”
.
2.7.3 10/100 Mbits/s Indication
The device can be programmed such that the operation speed (10 or 100
Mbits/s) appears on the PLED0n pin. To do this, appropriately set the
Programmable LED Output Select bits in the MI serial port Configuration
2 register as described in
Table 2.9
. When the PLED0n pin is pro-
grammed to be speed detect output, it is asserted LOW when the device
is configured for 100 Mbit/s operation. The PLED0n output has both pul-
lup and pulldown driver transistors and a weak pullup resistor, so it can
drive an LED from either V
DD
or GND and can also drive a digital input.