
Draft 6/5/00
10/100 Mbits/s Selection
2-39
Copyright 1999 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
Set the Speed Select (SPEED) bit in the MI serial port Control
register.
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 2.3.10, “Link Integrity and AutoNegotiation”
.
2.7.3 10/100 Mbits/s Indication
The channel 10/100 Mbits/s speed can be monitored through the
SPD_DET bit in the MI serial port Channel Status Output register.
In the MI serial port Configuration register, set the LED function select
bits (LED_DEF[1:0]) so that the 10/100 speed condition is indicated at
the PLED0n output. Set the PLED_2[1:0]n bits in the same register to
0b11 (normal). When the PLEDn0 pin is programmed to be a speed
detect output, it is asserted LOW when the device is configured for 100
Mbits/s operation. The PLED0n output has both pullup 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.
See
Section 2.3.13, “LED Drivers,” page 2-31
for more details on how to
program the LED output pins to indicate various conditions.