Micromod RetroPAK: SLC Installation Manual - Manual (Page 64)

SLC RetroPAK Controller
COMMUNICATIONS CONNECTIONS
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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
The RetroPAK controller is set up to provide Modbus RS-232 communications through the
front port on the front panel assembly. This allows download of configured databases from a
portable computer using the downloading cable 109S1854.
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 front panel.
The transmission mode of Modbus networks using either the built-in circuits is RTU (Remote
Terminal Unit).
Addresses
Each slave on a Modbus network must have a unique address. Addresses 1 through 247 (01
through f7 in hexadecimal) are supported by the Modbus protocol. Addresses for the built-in
circuit are assigned by configuration of a data base attribute. Addresses for modular circuits
are set at the module as shown in Figure 5-7.
5.5.2 RS-232 Modbus Communication
The built-in circuit for RS-232 communication uses a driver/receiver which supports a point-
to-point Modbus network. These circuits meet all RS-232C and V.28 specifications. They
have a±9V output swing with a+5V supply, and±30V receiver input levels. All field
connection terminals are optically isolated from the instrument circuitry. The maximum
network cable length is 50 feet.
The circuit supports the Extended Modbus protocol which provides full communications
functionality between the controllers and the Visual Application Designer software.