schneiderModbus Master (Serial and TCP/IP) Driver for Field Device System Integrator Modules

addresses in DCI blocks, the Modbus driver 

automatically determines the necessary transactions.

After the appropriate DCI blocks and ECBs are 

configured and device communication is enabled, the 

FDSI FBM starts sending “scan” messages to each 

Modbus device. The FBM waits for a response from 

the device, processes the data contained in the 

response, and stores the data in its database for 

incorporation into the I/A Series control system. Data 

can also be written out to the individual devices from 

the I/A Series network.

Installation and Download

Installation of the driver does not require shutting 

down the I/A Series software or rebooting the 

I/A Series workstation. Furthermore, any updated 

driver can be downloaded to the FBM or FBM pair 

without disrupting the rest of the I/A Series system.

CONFIGURATION

To configure the FDSI Modbus Master driver, you 

must use the FDSI Configurator software, which can 

be installed on a workstation running the 

Windows XP® operating system. The FDSI 

Configurator is required for configuring FBM serial 

and Ethernet port properties and communication 

settings. 

Device Configuration

Device configuration for the Modbus Master driver is 

performed entirely in DCI blocks. There are no scan 

ECBs or device configuration files required or used 

by the driver. Once you have configured DCI blocks, 

the driver builds the required Modbus scan 

transactions to transfer data. 

SPECIFICATIONS

Protocols

The Modbus Master driver offers support for the 

following protocols:

 Modbus RTU protocol (for serial devices)

 Modbus ASCII protocol (for serial devices)

 Modbus/TCP protocol (for Ethernet devices)

For additional information, refer to the following 

Modbus protocol documentation:

 Modicon Modbus Protocol Reference Guide

(Modbus RTU and Modbus ASCII protocols) 

PI-MBUS–300 Rev. J, MODICON, Inc. Industrial 

Automation Systems, June 1996 

 Open Modbus/TCP Specification (Modbus/TCP 

protocol) Release 1.0, Schneider Electric, 

March 1999.

Register Address Support

The Modbus Master driver supports both five digit 

and six digit register addresses.

Data Type and Format

The Modbus Master driver accepts data from 

devices in big endian or little endian format; data 

format is configurable. 

Number of Devices

Up to 64 devices per FDSI FBM maximum. The 

number of actual devices is performance and 

configuration dependent.

Number of Devices per FBM

 RS-232: 1 device per port

 RS-422: 1 device per port

 RS-485: 16 devices per port

 Ethernet: multiple devices per FBM or FBM pair. 

(The number of actual devices is performance 

dependent.)

Number of Points

Up to 2000 I/O points can be handled in an FDSI 

FBM. The standard Modbus Master driver uses a 

default 500 millisecond scan cycle, but can be 

configured to other rates in 100 ms increments to as 

fast as 100 ms. As a result, the practical limit on the 

number of points that can be supported depends on 

the update rate you require. The throughput rate is 

determined by:

 Network limitations.

 Efficiency of the database (accessing scattered 

registers in a Modbus device requires more 

Modbus messages than accessing contiguous 

register numbers).

 Response time of the connected devices.

Control Block Support

Distributed Control Interface (DCI) blocks address 

and read/write data from/to the addressed slave 

device. The Modbus driver offers control block 

support for the following ECBs and standard DCI 

block types:

Table 1. ECBs Supported by the Modbus 

Master Driver

ECB200 Parent ECB, representing the FBM230 

or FBM232

ECB202 Parent ECB, representing the FBM231 

or FBM233

ECB201 Child ECB, representing a device

Table 2. DCI Blocks Supported by the Modbus 

Master Driver

BIN Binary Input block

BINR Redundant Binary Input block

BOUT Binary Output block

IIN Integer Input block

IOUT Integer Output block

PAKIN Packed Input block

PAKOUT Packed Output block

PLSOUT Pulse Output block

RIN Real Input DCI block

RINR Redundant Real Input DCI block

ROUT Real Output DCI block