Draft 6/5/00
Block Diagram Description
2-23
Copyright 2000 by LSI Logic Corporation. All rights reserved.
2.2.7.4 Transmit Rise and Fall Time Adjust
The transmit output rise and fall time can be adjusted with the two
Transmit Rise/Fall time adjust bits (TRF[1:0]) in the MI serial port
Configuration 1 register. The adjustment range is
0.25 ns to +0.5 ns in
0.25 ns steps.
2.2.7.5 STP (150 Ohm) Cable Mode
The transmitter can be configured to drive 150
shielded twisted-pair
cable. To enable this configuration, set the Cable Type Select bit
(CABLE) in the MI serial port Configuration 1 register. When STP mode
is enabled, the output current is automatically adjusted to comply with
IEEE 802.3 levels.
2.2.7.6 Transmit Activity Indication
Appropriately setting the programmable LED Output Select bits in the MI
serial port LED Configuration 2 register programs transmit activity to
appear on some of the PLED[5:0]n pins. When one or more of the
PLED[5:0]n pins is programmed to be an activity or transmit activity
detect output, that pin is asserted LOW for 100 ms every time a transmit
packet occurs. The PLED[5:0]n outputs are open-drain with resistor
pullup and can drive an LED from V
DD
or can drive other digital inputs.
See
Section 2.2.14, “LED Drivers,” page 2-37
for more detailed
information on the LED outputs.
2.2.7.7 Transmit Disable
Setting the Transmit Disable bit (XMT_DIS) in the MI serial port
Configuration 1 register disables the TP transmitter. When the bit is set,
the TP transmitter is forced into the idle state, no data is transmitted, no
link pulses are transmitted, and internal loopback is disabled.
2.2.7.8 Transmit Powerdown
Setting the Transmit Powerdown bit (XMT_PDN) in the MI serial port
Configuration 1 register powers down the TP transmitter. When the bit is
set, the TP transmitter is powered down, the TP transmit outputs are high
impedance, and the rest of the L80223 operates normally.