VSC8601 Datasheet
Functional Descriptions
The VSC8601 device’s algorithm for HP Auto-MDIX successfully detects, corrects, and
operates with any of the MDI wiring pair combinations listed in the following table.
Table 2.
Supported MDI Pair Combinations
RJ-45 Pin Pairings
1, 2
A
3, 6
B
4, 5
C
7, 8
D
Mode
Normal MDI
B
A
D
C
Normal MDI-X
A
B
D
C
Normal MDI with pair swap on C and D pair
Normal MDI-X with pair swap on C and D pair
B
A
C
D
Note The VSC8601 device can be configured to perform HP Auto-MDIX even when its
auto-negotiation feature is disabled (setting register 0.12 to 0) and the link is forced
into 10/100 speeds. To enable this feature, set register 27E.15 = 0.
3.7
Link Speed Downshift
For operation in cabling environments that are incompatible with 1000BASE-T, the
VSC8601 device provides an automatic link speed “downshift” option. When enabled,
the device automatically changes its 1000BASE-T auto-negotiation advertisement to
the next slower speed after a set number of failed attempts at 1000BASE-T.
This is useful in networks using older cable installations that may include only pairs A
and B and not pairs C and D.
To configure and monitor link speed downshifting, use register bits 20E.4:1. For more
information, see “Extended PHY Control Set 1,” page 50.
3.8
3.9
Transformerless Ethernet
The Cat5 media interface supports 10/100/1000BT Ethernet for backplane applications
such as those specified by the PICMGTM 2.16 and ATCATM 3.0 specifications for
eight-pin channels. With proper AC coupling, the typical Cat5 transformer can be
removed and replaced with capacitors.
Ethernet Inline Powered Devices
The VSC8601 device can detect inline powered devices in Ethernet network
applications. Its inline powered detection capability can be part of a system that allows
for IP-phone and other devices, such as wireless access points, to receive power
directly from their Ethernet cable, similar to office digital phones receiving power from
a Private Branch Exchange (PBX) office switch over the telephone cabling. This can
eliminate the need for an IP-phone to have an external power supply. It also enables
the inline powered device to remain active during a power outage (assuming the
Ethernet switch is connected to an uninterrupted power supply, battery, back-up power
generator, or some other uninterruptible power source).
For more information about inline powered device detection, visit the Cisco Web site at
www.cisco.com.
Revision 4.1
September 2009
Page 21
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
