VSC8658 datasheet(31/95 Pages) MICROSEMI

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Functional Descriptions

VMDS-10242 VSC8658 Datasheet Revision 4.1

When using the connector loopback testing feature, the device auto-negotiation, speed, and duplex

configuration is set using device registers 0, 4, and 9. For 1000BASE-T connector loopback, only the

following additional writes are required. Execute the additional writes in the following order:

Enable the 1000BASE-T connector loopback. Set register bit 24.0 to 1.

Disable pair swap correction. Set register bit 18.5 to 1.

4.16.6

VeriPHY Cable Diagnostics

The VSC8658 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.

Note: If a link is established on the twisted pair interface in the 1000BASE-T mode, VeriPHY can run without

disrupting the link or disrupting 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 re-established.

The following diagnostic functions are part of the VeriPHY suite:

•

Detecting coupling between cable pairs

•

Detecting cable pair termination

•

Determining 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. All

these conditions can prevent the device from establishing a link in any speed.

Cable Pair Termination Proper termination of Cat5 cable requires a 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.

4.16.7

IEEE 1149.1 JTAG Boundary Scan

The VSC8658 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 VSC8658 device, accessed using its TAP interface, consists of a

boundary scan register and other logic control blocks. The TAP controller includes all IEEE-required

signals (TMS, TCK, TDI, and TDO), in addition to the optional asynchronous reset signal NTRST.

The following illustration shows the TAP and Boundary Scan Architecture.

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