VSC8658 datasheet(30/95 Pages) MICROSEMI

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Functional Descriptions

VMDS-10242 VSC8658 Datasheet Revision 4.1

•

After receiving a packet on the media interface, register bit 18E.15 is set and cleared after being

read. The packet then is counted by either the good CRC counter or the bad CRC counter. Both

CRC counters are also automatically cleared when read.

•

The good CRC counter’s highest value is 10,000 packets. After it reaches this value, the counter

clears and continues to count additional packets beyond that value. The bad CRC counter stops

counting when it reaches its maximum counter limit of 255 packets.

4.16.3

Far-End Loopback

The far-end loopback testing feature is enabled by setting register bit 23.3 to 1. When enabled, it forces

incoming data from a link partner on the current media interface to be retransmitted back to the link

partner on the media interface as shown in the following illustration. In addition, the incoming data also

appears on the receive data pins of the MAC interface. Data present on the transmit data pins of the

MAC interface is ignored when using this testing feature.

Figure 13 •

Far-End Loopback Diagram

4.16.4

Near-End Loopback

When the near-end loopback testing feature is enabled (by setting the device register bit 0.14 to 1), data

on the transmit data pins (TXD) is looped back onto the device receive data pins (RXD), as shown in the

following figure. When using this testing feature, no data is transmitted over the network.

Figure 14 •

Near-End Loopback Diagram

4.16.5

Connector Loopback

The connector loopback testing feature allows the twisted pair interface to be looped back externally.

When using this feature, the PHY must be connected to a loopback connector or a loopback cable. Pair

A should be connected to pair B, and pair C to pair D, as shown in the following figure. The connector

loopback feature functions at all available interface speeds.

Figure 15 •

Connector Loopback Diagram

Link Partner

PHY_Port_n

MAC

RXD

TXD

Cat5

Link Partner

PHY Port_n

MAC

RXD

TXD

Cat5

PHY Port_n

MAC

RXD

TXD

Cat5

VSC8658 Datasheet(PDF) 30 Page - Microsemi Corporation

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