When interfacing to the E1 line with Secondary Over Voltage protection or in a high return loss configuration, resistors are added between the DS2153 outputs and the transformer. Normally the resistors are of different values depending on whether the interface is driving a 75Ω coax or 120Ω twisted wire pair line. Also a change in the termination resistor is required. A single set of resistors can be utilized in both situations by using the circuit shown in Figure 1
. The dotted lines indicate jumper positions for selecting 75Ω or 120Ω operation.
Figure 1. E1 interface.
Table 1. Line Interface Control Register Settings
- Transformers shown are available from Pulse.
- Resistors shown are within 1" of best value.