VSC8601 Datasheet
Functional Descriptions
connector loopback, only the following additional writes are required. Execute the
additional writes in the following order:
1. Enable the 1000BASE-T connector loopback. Set register bit 24.0 to 1.
2. Disable the pair swap correction. Set register bit 18.5 to 1.
3.13.6
VeriPHY Cable Diagnostics
The VSC8601 device includes a comprehensive suite of cable diagnostic functions that
are available using SMI reads and writes. These functions enable a variety of cable
operating conditions and status to be accessed and checked. The VeriPHY suite has the
ability to identify the cable length and operating conditions and to isolate a variety of
common faults that can occur on the Cat5 twisted pair cabling.
For more information, refer to the PHY API Software and Programmers Guide on the
Vitesse Web site at www.vitesse.com.
Note If a link is established on the twisted pair interface in 1000BASE-T mode,
VeriPHY can run without disrupting the link or any data transfer. However, if a link is
established in 100BASE-TX or 10BASE-T, VeriPHY causes the link to drop while the
diagnostics are running. After the diagnostics are finished, the link is then
re-established.
The following diagnostic functions are part of the VeriPHY suite:
•
•
•
Detection of coupling between cable pairs
Detection of cable pair termination
Determination of cable length
Coupling Between Cable Pairs Shorted wires, improper termination, or high
crosstalk resulting from an incorrect wire map can cause error conditions, such as
anomalous coupling between cable pairs. These conditions can all prevent the device
from establishing a link at any speed.
Cable Pair Termination Proper termination of Cat5 cable requires 100-Ω differential
impedance between the positive and negative cable terminals. The IEEE standard 802.3
allows for a termination of as high as 115 Ω or as low as 85 Ω. If the termination falls
outside of this range, it is reported by the VeriPHY diagnostics as an anomalous
termination. The diagnostics can also determine the presence of an open or shorted
cable pair.
Cable Length When the Cat5 cable in an installation is properly terminated, VeriPHY
reports the approximate cable length in meters.
3.13.7
IEEE 1149.1 JTAG Boundary Scan
The VSC8601 device supports the Test Access Port (TAP) and boundary-scan
architecture described in the IEEE standard 1149.1. The device includes an IEEE
1149.1-compliant test interface, often referred to as a “JTAG TAP Interface.”
The JTAG boundary-scan logic on the VSC8601 device, accessed using its TAP interface,
consists of a boundary-scan register and other logic control blocks. The TAP controller
Revision 4.1
September 2009
Page 33
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