# Testing in loopback mode

Use a loopback configuration for your CG 6565C board to test your digital trunk application without actually connecting to the telephone network.

Use a signal entry panel (SEP) or a punchdown block with eight RJ-48C trunk connectors. Connect a crossover cable for each transition board trunk connector to set up the loopback configuration. Connect a shielded 50-pin Telco cable to connect the CG 6565C to the signal entry panel or punchdown block.

The crossover cable connects the transmit signals from one trunk to the receive signals on another trunk.

The following illustration shows the CG 6565C loopback configuration with two punchdown blocks connecting trunks 7 and 8, 15 and 16, as well as 5 and 13 using crossover cables:

Each of the RJ-48C interfaces has the following pinouts:

The following illustration shows how the interface is wired on a loopback cable: