Installation guide

50 Elements of Network Planning
890 USE 100 00
2.2.3 Modbus Plus Tap
A tap is required at each site on the trunk cable to provide connections
for the trunk cable and drop cable. Its Modicon part number is
990NAD23000.
You should plan to order a sufficient quantity of taps and drop cables to
allow extra ones for service access and spares.
2.2.4 Modbus Plus Cable Impedance Termination
Each tap contains an internal terminating resistor that can be
connected by two jumpers. Two jumper wires are included in the tap
package, but are not installed. At the taps at the two ends of a cable
section, you must connect both of the jumpers to provide the proper
terminating impedance for the network. Taps at inline sites must have
both jumpers removed. Chapter 1 describes the meaning of cable
sections, end and inline sites.
The impedance is maintained regardless of whether a node device is
connected to the drop cable. Any connector can be disconnected from
its device without affecting the network impedance.