General Modbus Rtu Rs-485 Wiring Considerations; Setup Details (Using Modbus Poll As An Example); Figure 17. Serial Modbus Network Wiring Example; Figure 18. Serial Connection Wiring Ground To Controller - Siemens VersiCharge AC 8EM1312-4AF10-0AA3 Installation And Operation Manual

3.7.4 General ModBus RTU RS-485 wiring
considerations
Devices connected on the ModBus RTU, including the
Child, converter(s) and other instrumentation, must be
wired as follows:
• Connect the shield of each cable segment to ground at
one end only.
• Isolate cables, as much as possible, from sources of
electrical noise.
• Install a ¼ Watt termination resistor (RT) between the (+)
and (-) terminals of the device at each end point of a
straight-line bus. The resistor should match the nominal
impedance of the RS-485 cable, which is typically 120
ohms (consult the manufacturer's documentation for the
cable's impedance value).
RS-485 Connection methods to avoid
Any device connection that causes a branch in the main
RS-485 ModBus cable should be avoided. This includes star
and tee (T) methods. These wiring methods cause signal
reflections that may result in interference. No more than
two cables should be connected at any connection point
on the RS-485 ModBus daisy chain. This includes
connection points on instruments, converters, and
terminal strips. Following these guidelines ensures that
both star and tee connections are avoided.

Figure 17. Serial modbus network wiring example

Installation and Operations Manual

Figure 18. Serial connection wiring ground to controller

Setup for Modbus RTU communications see Figure 19 above.
ModBus RTU Implementation Limitations (see the table
below).
Function Codes Supported a.
b.
c.
Max number of units to be 24
connected by the ModBus
Controller
Max Length of wire 4000 ft
Polling Rate 1S (Min 500mS)

3.7.4.1 Setup Details (Using ModBus Poll as an example)

a. Connect RS 485 cable between PC and EVSE
VersiCharge using ModBus cable and connector (see
ModBus Connection).
b. Go to Connection->Connect as shown in next image.
| VersiCharge™ AC
0x03(Multiple register read group wise
with valid length of the read group)
0x10 (Multiple register write, parameter
wise),
0x11(Broadcast). – Condition is to have a
single unit connected on ModBus
17