Chapter 1 Ch1

User Manual: Chapter 1 Terminator I/O MODBUS Base Controller User Manual

Open the PDF directly: View PDF .
Page Count: 6

1

Introduction 1

In This Chapter. . . .

— Manual Overview

— Introduction to MODBUS

— Terminator I/O System

— T1K–MODBUS Base Controller

Introduction

Installation and

Safety Guidelines

1–2 Introduction

Manual Overview

This manual describes the installation and

operation of the Terminator I/O MODBUS

Base Controller (T1K–MODBUS).

The following manuals are essential to the proper use of your Terminator I/O

MODBUS Base Controller.

•Terminator Installation and I/O Manual part number T1K–INST–M

This manual contains very important information, including a complete

I/O Module Memory Map. The Memory Map is crucial in designing and

implementing a Terminator I/O system.

•The PLC User Manual (if PLC is used as master).

•The MODBUS Master manual (if other than PLC is used as master).

If you have a working knowledge of MODBUS networks, and the PLC or PC which

you are using, this manual will help you configure and install your T1K–MODBUS

Base Controller.

We strive to make our manuals the best in the industry and rely on your feedback in

reaching our goal. If you cannot find the solution to your particular application, or, if

for any reason you need additional technical assistance, please call us at

770–844–4200.

Our technical support team is glad to work with you in answering your questions.

They are available weekdays from 9:00 a.m. to 6:00 p.m. Eastern Time. We also

encourage you to visit our website where you can find technical and nontechnical

information about our products and our company.

www.automationdirect.com

The Purpose of

this Manual

Supplemental

Manuals

Who Should Read

this Manual

Technical Support

Introduction Installation and

Safety Guidelines

1–3

Introduction

The contents of this user manual are as follows:

Chapter Title What’s covered

Introduction introduces MODBUS and describes both the Terminator

I/O System and the T1K–MODBUS Base Controller

T1K–MODBUS

Specifications

provides module specifications, dip switch settings, port

pin–outs and wiring information.

MODBUS RTU Functions

and Addressing Modes

provides MODBUS RTU functions supported and use

with DirectLogic PLCs, or MODBUS 584/984 modes.

Using T1K–MODBUS

Setup Tool

explains how to configure the MODBUS port using the

Setup Tool.

Additional reference information for the T1K–MODBUS is available in the following

appendices.

Appendix Title What’s covered

I/O Module

Hot Swap explains the T1K–MODBUS I/O module Hot Swap feature

and the Enable/Disable Outputs switch.

Analog Output Module

Configuration uses a memory map to explain how to configure an analog

output module.

The “note pad” icon in the left–hand margin indicates a special note.

The “exclamation mark” icon in the left-hand margin indicates a warning or caution.

These are very important because the information may help you prevent serious

personal injury or equipment damage.

The “light bulb” icon in the left-hand margin indicates a tip or shortcut.

Manual Layout

1

2

3

4

Appendices

A

B

Symbols Used

Introduction

Installation and

Safety Guidelines

1–4 Introduction

Introduction to MODBUS

MODBUS RTU (Remote Terminal Unit) Protocol is a messaging structure used to

establish master–slave communications between intelligent devices. When a

MODBUS master sends a message to a MODBUS slave, the message contains the

address of the slave, the function, the data and a check sum. The slave’s response

message contains fields confirming the master’s request, any data requested and

an error–checking field.

A typical MODBUS RTU frame consists of the following fields:

ADDRESS FUNCTION DATA CHECKSUM

The address field of a message contains 8 bits. Valid slave addresses are in the

range of 0– 247 decimal. The individual slave devices are set in the range of 1 – 247

decimal (address 0 is the broadcast to all slaves address). The master specifies a

slave by placing the slave address in the address field of the message. When the

slave responds, it places its own address in the address field to identify to the master

which slave is responding.

The function code field of a message contains 8 bits. Valid function codes are in the

range of 1 – 255 decimal. The function code instructs the slave what kind of action to

take. Some examples are to read the status of a group of discrete inputs; to read the

data in a group of registers; to write to an output coil or a group of registers; or to read

the diagnostic status of a slave.

When a slave responds to the master, it uses the function code field to indicate either

a normal response or that some type of error has occurred. For a normal response,

the slave echoes the original function code. In an error condition, the slave echoes

the original function code with its MSB set to a logic 1.

The data field is constructed using sets of two hexadecimal digits in the range of 00

to FF. According to the network’s serial transmission mode, these digits can be made

of a pair of ASCII characters or from one RTU character.

The data field also contains additional information that the slave uses to execute the

action defined by the function code. This can include internal addresses, quantity of

items to be handled, etc.

The data field of a response from a slave to a master contains the data requested if

no error occurs. If an error occurs, the field contains an exception code that the

master uses to determine the next action to be taken. The data field can be

nonexistent in certain types of messages.

The checksum field is used for error checking. Standard MODBUS serial networks

use two types of error checking.

Parity checking (even or odd) totals the number of logical 1 bits in the data field and

sets the parity bit to a 0 or 1 representing an odd or even total of logical 1 bits. Cyclical

Redundancy Check (CRC) checks the entire message and is applied regardless of

any parity check method used. The CRC field consists of two bytes, creating a 16 bit

binary value. The CRC is calculated in the transmitting device and is recalculated

and compared by the receiving device.

Both the character check and the message frame check are generated in the master

device and applied to the message before transmission. The slave device checks

each character and the entire message frame during receipt.

Introduction Installation and

Safety Guidelines

1–5

Introduction

Terminator I/O System

Terminator I/O is a modular system which combines the functions of terminal blocks

and I/O modules for distributed I/O. Each Terminator I/O system has the following

components: a Power Supply, a Base Controller, and one or more I/O Modules and

I/O bases.

Power Supply

MODBUS

Base

Controller I/O Modules

I/O Base

I/O Module

Introduction

Installation and

Safety Guidelines

1–6 Introduction

T1K–MODBUS Base Controller

The T1K–MODBUS Base Controller is a slave module that functions as a controller

for Terminator I/O on a MODBUS network.

Note: It is recommended to use the T1K–MODBUS Base Controller in a “scan

based” (polled) control system rather than in an “event–driven” control system. As a

slave, the Base Controller does not have the ability to report an error condition to the

MODBUS network master. Thus, polling a slave on a regular basis will detect a slave

error condition promptly, whereas an event–driven control system will not detect a

slave error condition until the next event is addressed to a slave in error.

The Base Controller has the following features:

•Status LEDs

•MODBUS Port

•Serial Port (RJ12)

•Unit Address Switches

•Output Enable/Disable Switch

•DIP Switch (located on right side of unit)

Status LEDs

Unit Rotary

Address

Switches

Output

Enable/Disable

Switch

RJ12

Serial Port

MODBUS Port

MODBUS Base

Controller Features