Micromod MOD: 30ML Installation - Manual (Page 87)

MOD 30ML Multiloop Controller
COMMUNICATIONS CONNECTIONS
5.4.3 Termination
One set of ICN termination resistors must be installed on each ICN to prevent noise from
being picked up by the ICN circuitry and generating a diagnostic alarm. The ICN termination
scheme requires a nominal 24 volt DC power supply that can supply 15.4 mA. This supply is
provided by both the built-in and modular circuits. The termination resistor network is
provided in a 2030FZ00001A ICN Terminator. The terminator can be conveniently
connected to an ICN at built-in terminals 2 - 5 as shown in Figure 5-3. Note that the
terminator is connected to common via terminal 4 which is internally connected to terminal 1
(communications common) for ICN communication. The terminator can also be connected at
the appropriate four terminals when a communications module is used.
Other factors affecting the termination scheme are as follows.
 The ICN cable shields should be connected directly to chassis ground at one end only.
 Be sure each network has only one terminator. If the controller is connected to an
existing MOD 30 ICN, the network is already terminated and a terminator must not be
connected to any new device.
5.5 MODBUS NETWORK CONNECTIONS
5.5.1 General
Numerous Modbus network connection arrangements are possible. Selection of a specific
arrangement depends on the requirements of the application. The connection diagrams
shown in this section provide typical examples of connection schemes which meet all the
functional requirements of the Modbus protocol and the built-in and modular communication
circuits.
Master and Slave Designations
The controller can function as either a Modbus master or Modbus slave. This functionality is
determined by the configuration of the MSC block.
Communications Parameters
The baud rates available are: 150, 300, 600, 1200, 2400, 4800, 9600, 19200 or 38400.
Parity can be none, even or odd, and there can be either 1 or 2 stop bits. These parameters
are configurable via the MSC block.
The transmission mode of Modbus networks using either the built-in or modular circuits is
RTU (Remote Terminal Unit).
RS-485 Network Considerations
The RS-485 specification allows as many as 32 devices on any given network. The number
of devices can be increased by the use of repeaters. The Modbus network supports as many
as 247 slave devices.
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