VSC8221 datasheet(52/138 Pages) MICROSEMI

52 / 138 page

VSC8221

Data Sheet

VMDS-10106 Revision 4.1

December 2006

52 of 52

17.4 Near-End Loopback

When Near-end loopback is set (Mii Register bit 0.14 = 1), the Transmit Data (TDP/TDN) on the MAC interface is looped back

onto the Receive Data (RDP/RDN) pins to the MAC as shown in the figure below. in this mode, the CAT-5 media link is dropped.

Figure 19. Near-end Loopback Block Diagram

17.5 Connector Loopback

Connector Loopback allows for the twisted pair interface to be looped back externally. in this mode the PHY must be connected

to a loopback connector or a loopback cable. For this loopback, pair A should be connected to the corresponding wire of pair B

using a 100

Ω resistor, and each wire of pair C should be connected to the corresponding wire of pair D using a 100Ω resistor.

This loopback will work in all speeds selected for the interface.

Figure 20. Connector Loopback

The auto-negotiation, speed, and duplex can be configured using Mii registers 0,4 and 9. For 1000BT connector loopback only

the following additional writes are required in the specific order.

1. Master/Slave configuration forced to Master (Mii Register Bits 9.12:11 = 11)

2. Enable 1000BT connector loopback (Mii Register 24.0 = 1)

3. Disable pair swap correction (Mii Register Bit 18.5=1)

4. Disable auto-negotiation and force 1000BT link (Mii Register Bit 0.12=0, Mii Register Bit 0.6=1, and Mii Register Bit 0.12=0)

and force either full or half duplex (Mii Register Bit 0.8=0 or 1).

This loopback is also available in the 100BASE-FX mode.

Link Partner

VSC8221

Serial

MAC

RDP/RDN

TDP/TDN

CAT-5 or Fiber

VSC8221

Serial

MAC

RDP/RDN

TDP/TDN

VSC8221 датащи(PDF) 52 Page - Microsemi Corporation