FOXBORO FBM224 Modbus® Communication Module

FOXBORO FBM224 Modbus® Communication Module

DESCRIPTION

The FBM224 Modbus Communication Interface Module provides an interface between Modbus slave devices — such as programmable logic controllers and field I/O devices — and the Control Processor (FCP280, FCP270/ZCP270, or CP60) of the Foxboro Evo™ Process Automation System or I/A Series system. Devices with which the FBM224 can successfully communicate are those which support RS-232, RS-422, or RS-485 communication interface standards and the Modbus protocol in RTU mode.

FEATURES Key features of the FBM224 module are: 

 Conforms to Modbus protocol 

 Offers a choice of RS-232, RS-422, or RS-485 communication interface standard 

 Integrates Modbus slave device data into a Foxboro control database 

 With its associated termination assembly (TA), is suitable for installation in Class 1, Division 2 and Zone 2 locations.

SERIAL LINK SETUP

Data communication between the FBM224 and Modbus slave devices are through the 4-ported termination assembly (TA). The TA has compression terminals for each port for RS-422 and RS-485 wiring, with DIP-switch-selectable bus termination resistors per port. For RS-232 wiring, the TA has a standard DB-25 male connector and a break-out bank of 24 DIP switches for each port that can be used for any RS-232 wiring configuration (for example, to connect Clear-to-Send to Request-toSend).

CONFIGURATORS

Two configurators are provided, Windows® or Solaris® versions, for the setup of FBM224 port and slave configuration files. The port configurator allows for easy setup of the communication parameters for each port (such as, communication interface standard, baud rate, parity). The device transaction configurator allows for easy setup of the transaction specifications for slave device files (such as, scan rate, function code, start address of the data to be transferred, and the amount of data to be transferred in one transaction). Up to 64 separate transactions can be specified for each Modbus device. During configuration, the selected values and supported options are automatically checked for range validity.

OPERATIONS

Each FBM224 can access up to 64 devices to read or write data.

From the Foxboro control station to which the FBM224 is connected (refer to Figure 2), up to 2000 Distributed Control Interface (DCI) data connections can be made to read or write data. A connection can be to:

 An analog input or output value (integer or IEEE single-precision floating point) 

 A single digital input or output value 

 Multiple (packed) digital input or output values (packed in groups of up to 32 digital points per connection).

PHASE AND SCAN RATE

During a basic scan cycle, the FBM224 performs all scheduled read/write transactions to each Modbus device. Users can adjust the Scan Rate and Phase for each cycle to reduce the loading on the FBM224 and/or on the Modbus device. The Scan Rate specifies the periodic processing of device transactions as a multiple of the basic scan cycle. The default is 500 ms. The range is {500 ms, 1 sec, 2 sec, and so forth, up to 255 sec}. The Phase specifies the exact scan cycle to perform the device transactions when the Scan Rate is a multiple of the basic scan cycle.

STANDARD DESIGN

The FBM224 has a rugged extruded aluminum exterior for physical and electrical protection of the circuits. Enclosures, specially designed for mounting the FBMs, provide various levels of environmental protection, up to harsh environments per ISA Standard S71.04.

EASY REMOVAL/REPLACEMENT

The module can be removed or replaced without removing field device termination cabling, power, or communications cabling.

FIELDBUS COMMUNICATION

A Fieldbus Communications Module or a Control Processor interfaces to the redundant 2 Mbps module Fieldbus used by the FBMs. The FBM224 accepts communication from either path (A or B) of the redundant 2 Mbps Fieldbus — should one path fail or be switched at the system level, the module continues communication over the active path.