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6-18 CHAPTER 6: DIAGNOSTICS AND TROUBLESHOOTING
RJ-45 Loopback Plug
To construct an external loopback plug for use in testing the
unshielded twisted-pair version of the ATMLink PCI NIC
(3C975-UTP), use an RJ-45 unshielded male connector.
Wire the loopback plug so that the transmit output of the
NIC (connector pins 1 and 2) is directly wired to the NIC’s
receive input (connector pins 7 and 8, respectively), as shown
in Figure 6-12. See Appendix A for a complete table of pinouts
for the 3C975-UTP NIC.
Figure 6-12 UTP External Loopback Plug
Receive (+) 7
Transmit (+) 1 Receive (–) 8
Transmit (–) 2
RJ-45 unshielded
male connector