ICPDAS ALM-06-WF User Manual

ALM-06-WF User’s Manual

www.icpdas.com

Warranty

All products manufactured by ICP DAS are under warranty regarding defective materials for a period of one year from the date of delivery to the original purchaser.

Warning

ICP DAS assumes no liability for damages resulting from the use of this product. ICP DAS reserves the right to change this manual at any time without notice. The information furnished by ICP DAS is believed to be accurate and reliable. However, no responsibility is assumed by ICP DAS for its use, or for any infringements of patents or other rights of third parties resulting from its use.

Trademark

The names used for identification only may be registered trademarks of their

respective companies.

ALM-06-WF User’s Manual (Rev1.0, Feb./2019) ------------- 1

ALM-06-WF User’s Manual

Document Revision

Version Date Description of changes

Rev1.0 2019-05-17 First release for ALM-06-WF

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ALM-06-WF User’s Manual

Table of Contents

1. Introduction .......................................................................................... 5

1.1 Wireless connection mode ................................................................... 5

1.2 Features .............................................................................................. 5

1.2.1 Features Description ........................................................................ 6

1.3 Specifications ...................................................................................... 7

2. Hardware.............................................................................................. 9

2.1 Outward Appearance .......................................................................... 9

2.1.1 LED Indicator ................................................................................. 10

2.1.2 Connector Pin Define ..................................................................... 10

2.2 Reset to default .................................................................................. 11

2.3 Dimensions ........................................................................................ 11

2.4 Wire Connection ............................................................................... 12

2.4.1 Wire connection define ................................................................... 12

2.4.2 I/O connection ................................................................................ 12

3. Software.............................................................................................. 14

3.1 ALM Utility(AP Mode) ..................................................................... 14

3.1.1 Main Screen ................................................................................... 14

3.1.2 Controller Status ............................................................................... 15

3.1.3 DI/DO Status & Control .................................................................... 15

3.1.4 Status Bar ........................................................................................ 15

3.1.5 Icon Button ...................................................................................... 16

3.1.6 Configuration/Setup ....................................................................... 17

3.2 Station Mode (STA) IP scanner ......................................................... 19

3.3 Alarm Mode & Audio Editor ............................................................. 20

3.4 Start your Edit .................................................................................. 21

3.4.1 Make a Micro SD from project ........................................................... 24

3.4.2 Insert a New MicroSD ....................................................................... 24

3.5 Alarm Mode Description ................................................................... 25

4. Application ......................................................................................... 29

4.1 Connection with Modbus TCP utility................................................. 29

5. Modbus Applications ........................................................................... 31

5.1 What is Modbus TCP/IP? ................................................................. 31

5.2 Protocol Description ......................................................................... 32

5.2.1 MBAP ............................................................................................. 32

5.2.2 Function Code .................................................................................. 33

5.2.3 Data ................................................................................................ 33

5.2.4 Response ......................................................................................... 34

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5.2.5 Data Encoding .................................................................................. 34

5.3 ALM-06-WF Address Mapping ......................................................... 35

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1. Introduction

The ALM-06-WF have WLAN connection complies with the IEEE802.11b/g/n standards. With the popularity of 802.11 network infrastructure, the ALM-06-WF make an easy way to incorporate wireless connectivity into monitoring and configuration. They also support Modbus TCP protocol and the network encryption configuration, which makes perfect integration to SCADA software and offer easy and safe access for users from anytime and anywhere.

Figure 1-1: Application architecture for the ALM-06-WF

1.1 Wireless connection mode

ALM-06-WF support both Access Point(AP) & Station(STA) wireless connection modes of WLAN.

1.2 Features

 Wi-Fi communication monitoring and configuration  Compatible with IEEE 802.11b/g/n standards  Support Access Point(AP, 1 Client) & Station(STA) modes for wireless networks  Support WEP, WPA and WPA2 wireless encryption  Support Modbus TCP monitoring  Support DHCP Server(AP), DHCP Client or Static IP(STA) network configuration  Wide operating temperature range  Wide power supply range  Photo couple input, Relay output  MP3 Audio Output, external Line out  Digital Volume control  8 Alarm mode support

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1.2.1 Features Description

The ALM-06-WF offers the most comprehensive configuration to meet specific application requirements. The following list shows the features designed to simplify installation, configuration and application.

Compatible with IEEE 802.11b/g/n standards

ALM-06-WF complied with IEEE 802.11b/g/n standard from 2.4~2.5 GHz, and it can be used to connect your wireless LAN.

Support Access Point(AP) & Station(STA) modes for wireless networks

AP mode lets you create a Limited AP(1 Client access allow) network with the specified SSID to communicate directly with each other without the need for a wireless access point.

STA mode is the more common network configuration where all wireless clients connect to the wireless network via a WAP (Wireless Access Point).

Support WEP, WPA and WPA2 wireless encryption

WEP and WPA are common types of security that are used to protect wireless networks. When WEP or WPA is turned on, ALM-06-WF uses a special security key combination to allow only devices that know this key to connect to its wireless network. This applies to laptops, smart device, or any other wireless device.

Support Modbus TCP protocols

The Modbus TCP server function on the ALM-06-WF can be used to provide data monitoring from HMI/SCADA software built with Modbus TCP driver.

Also there is some other HMI Modbus App in Android Google Play you can use.

Built-in MP3 Audio decoder & Output

The Alarm sound output using MP3(MPEG1-Audio Layer Ⅲ) audio, it support most

of MP3 format(Sample Rate 24/44.1(prefer)/48 KHz, Bit Rate 32 64 96 128(prefer) 160 192 Kbit/s), include an 3W audio power amplifier & 1KΩ Impedance Line Out can send

the alarm sound to external PA(Power Amplifier) system.

Support 6 channel trigger input with 8 alarm mode

Include 6 channel Photo couple input & 8 kinds of mode for trigger alarm, it also can be trigger an extend device using external Relay Output. All modes & MP3 audio files can be monitoring, configuration & download from PC Utility, it also can monitor status form Android APP.

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1.3 Specifications

Table 1-1: System Specifications

Wi-Fi Interface

Antenna Chip Antenna

Output Power 18.0 dBm @ 1 DSSS/14.5 dBm @ 54 OFDM

Receive Sensitivity –95.7 dBm @ 1 DSSS/–74.0 dBm @ 54 OFDM

Interface Wi-Fi 2.4G

Standard Supported IEEE 802.11b/g/n

Wireless Mode Station & AP (1 Client)

Encryption WEP, WPA and WPA2

Service TCP, Modbus TCP

LED Indicators

One 2 colors LED, Blue for System status,

Power/Status

Purple(Blue+Red)for Connective status/Locato

Isolation

Intra-module Isolation, Field-to-Logic

Protection

ESD (IEC 61000-4-2) ±8 kV Air for Random Point

EFT (IEC 61000-4-4) ±2 kV for Powe

Waterproof(IEC 60529) IP54 (Panel Mount Upright Position)

Power Requirements

Input Voltage Range 9 ~ 28 VDC with Reverse Protection (Vin to GND)

Power Consumption 0.7 W Standby.

Mechanism

Dimensions(WxLxH) 72 mm x 72mm x 22 mm

Installation Panel Mount/Wall Mount/DIN-Rail Mounting

Environment

Operating Temperature -20℃ ~ +75℃

Storage Temperature -30℃ ~ +85℃

Humidity 10% ~ 85% RH, Non-condensing

3000 VDC

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Table 1-2: I/O Specification

Digital Input

Channels 6

Input Type Dry Contact: Sink

Dry Contact Level

Photo-Isolation 3750 VDC

Input Condition Pulse Width must > 150mSec or more

Digital Output

Channels 1

Output Type Form A

Contact Rating (Resistive Load) DC50V/100mA

Off Voltage Level: Open

On Voltage Level: Close to GND

Table 1-3: Audio Specification

Audio

Sound Pressure Level 99dB@1KHz/1meter

Volume Control

Number of Playback

Audio File Format

Sample Rate

Bit Rate

Audio Startup Time

Audio Output

Line out Impedance

Digital Volume Control

64(Max)

MPEG1-Audio Layer Ⅲ (MP3)

24/44.1(prefer)/48 KHz

32 64 96 128(prefer) 160 192 kbit/s

< 150ms

3W(Max)

1KΩ

Table 1-4: Storage Specification

Storage

Audio Files Locate

File System

File Transfer

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Micro SD(T-Flash) up to 32GB, bundle 4GB

Fat16/32

PC Utility through Wi-Fi

ALM-06-WF User’s Manual

)

2. Hardware

2.1 Outward Appearance

ALM-06-WF contains I/O connectors, Micro SD, Reset to Default and LEDs.

Power/Status LED

Reset to Default Switch

Figure 2-1: Front Panel

Connecto

Figure 2-2: Back Panel

Micro SD(T-Flash

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2.1.1 LED Indicator

Table 2-1: System Status Indicator

System Status Indicator

LED Controller Status LED Status

Wi-Fi get Link Power On Blue LED

PWR

2.1.2 Connector Pin Define

Locator Red LED Blinking Process reset to default Blue LED Blinking(Fast) Alarm Status Red LED

Terminal NO Pin Name Wire Color

Purple(Blue + Red)

1 DI1 Brown

LED ON

2 DI2 Red

3 DI3 Orange

4 DI4 Yellow

5 DI5 Green

6 DI6 Blue 7 DI.GND Gray

8 Vin Red

9 Vin Red 10 GND Black

11 GND Black

12 Line Out Purple

13 RL White

14 RL White

Figure 2-3: I/O Connector of ALM-06-WF

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2.2 Reset to default

ALM-06-WF User’s Manual

Press & hold the reset button on the

LED quick flash then release to restore

bottom side over 6 Sec until the Red

ALM-06-WF default setting, default is

set in AP mode.

Figure 2-4: Reset button locate in the bottom side of ALM-06-WF

2.3 Dimensions

The diagrams below provide the dimensions of the ALM-06-WF to use in defining

your enclosure specifications. All dimensions are in millimeters.

Figure 2-5: Dimension of the ALM-06-WF

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2.4 Wire Connection

2.4.1 Wire connection define

The following describe the wire color & function

2.4.2 I/O connection

2.4.2.1 Digital Input (DI) wiring

Figure 2-6: Wire color & function

Figure 2-7: DI Dry contact wiring

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2.4.2.2 Relay Output wiring

Figure 2-8: Relay Output wiring

2.4.2.3 Line Out wiring

Figure 2-9: Line Out wiring

2.4.2.4 Power Input

Figure 2-10: Power Input

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3. Software

The ALM Utility provides the simple way to operating and acquire I/O status. ALM Utility can used the wireless network interface to configuration. Provide AP(Access Point) & STA(Station) mode to connect the ALM-06-WF.

ALM Utility available on both Windows & Android application to operating and configure the ALM-06-WF.

Utility Support Windows 7 (or later versions) and Android 5.0 (or later versions).

3.1 ALM Utility(AP Mode)

The following is the main screens provided by ALM Utility, these utility tools can be thought as a useful tool for configuration and monitoring on the ALM-06-WF. It supplies several functions, such as Monitoring, Configuration, Connection, Wi-Fi setting and F/W upgrade, etc.., Only PC Utility support Audio & Alarm Configuration.

3.1.1

Main Screen

Figure 3-1: ALM Utility main screen

(From left to right is Windows Utility , Android App)

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3.1.2 Controller Status

Show the connected controller information, user define Locate string, RSSI strength, Device IP & Static IP button for changing device IP in STA mode.

3.1.3 DI/DO Status & Control

Show the DI/Relay Output status, The value can be read(DI) or set(Relay Output) in this area.

Volume Control trackbar, range from 0(Mute)~10(Max).

Armed/DisArmed button for global alarm Enable/Disable. Audio Configuration icon enter the configuration page (Only in PC Utility).

3.1.4 Status Bar

Show the F/W Version, Device’s Alarm mode, SD capacity, MAC address and Device’s IP address.

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3.1.5 Icon Button

ICON function

Setup

Open the Setup Screen (Android versions Setup

function under the

icon)

Find Controller

Refresh

Controlle Refresh status

Only Android Device,

Red Led blinking, use to find the connected

Include setup, FW Version & About.

Audio

Configuration

Channel Test Simulation Channel Test. (Only in Android)

Audio Configuration page.

Table 3-1: icon Indicator

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3.1.6 Configuration/Setup

Click apply icon

AP：

SSID Name

1. Default Controller’s SSID in Wi-Fi AP mode, will be ALM-06-xxxxxx.

Key Type

SSID Key

STA：

SSID Name

Figure 3-2: ALM Utility setup page

to save each subject’s setting, after finish all setting click

to make device take effect on new setting

Note: xxxxxx is the last 6 characters MAC address of your device.

AP mode SSID Key type (default is Open)

AP mode SSID Key, (default is None)

Wi-Fi AP’s SSID intent to connect (default is tWFHUB)

Key Type

Wi-Fi AP’s SSID Key Type (default is WPA/WPA2)

SSID Key

Wi-Fi AP’s SSID Key (default is 00000000)

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Static IP: IP: Specific an IP that is not been used.

Mask: Default will be 255.255.255.0. Gateway: Basically define in the AP you are going to connect.

SSID

Key Type



Wi-Fi Mode：

Service Set Identifier: Connected devices must be the same SSID, SSID length must not exceed 31 characters. Key of Encryption, connected devices must with the same Key. Open ：No Key request.

WEP(Shared) ：Key length must be 15 characters. WPA/WPA2-PSK ：Key length must between 8~15 characters.

Table 3-2: Station SSID & Key type configure

ALM Controller working mode (default is in AP)

AP (Access Point)：

PC or Android Device connect to ALM Controller directly through AP(Fixed IP:192.168.77.1), AP mode support only one connection, If Multiple devices connect at a same time, only first connected devices can access.

STA(Station):

ALM Controller will auto connect to specific Wi-Fi AP, PC or Android Device also need to connect to the same AP, then they can use those ALM Controller in same domain.

*. Please check specific Wi-Fi AP is active and SSID/key is same as the setting before use.

Location information:

Set the information for you to identify & locate those Controller easily, length

must under 31 characters.

Modbus Port:

Modify Modbus TCP Port (default is 502)

   

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3.2 Station Mode (STA) IP scanner

There are lot of free IP scanner tools in both Windows & Android OS, for

example “Advanced IP Scanner” for Windows, “Network Analyzer” for Android,

those are high performance scanner tools on each OS.

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3.3 Alarm Mode & Audio Editor



ALM-06-WF contain 8 kinds of alarm mode, Mode 0 ~ 3 are DI1~DI6 in single independence channel trigger, in DIx channel priority, the priority of DI channel is DI6 > DI5... > DI1. Mode 4 ~ 7 are DI1~DI5 in Binary trigger & DI6 in single channel trigger, the priority of DI channel in this mode is DI6 > 11111b(0x1F)>…> 00001b(0x01).

Alarm Mode

Mode Channel Trigger Function Mode Binary Trigger Function

0 General Playback 4 General Playback 1 2 Hold Repeat Playbac 3 Memory Once Playback 7 Memory Once Playback

Trigger Input priority Playback

Max 4 MP3 files can be add for each Channel or Binary trigger alarm, it will playback from #1 to #4 for the trigger depend on the setting.

Relay output can set an extend alarm output to trigger other device.

All those setting can be done in PC Utility & can be monitor Armed/DisArmed on both PC Utility or Android APP, show as below.

5 Trigger Input priority Playback 6 Hold Repeat Playbac

Figure 3-3: ALM-06-WF PC Utility Audio Editor page.

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3.4 Start your Edit

Follow the step number,

(1) Select Job: Select Project or Device to Edit.

If Project Edit selected, you need to save project after finish edit.

In Device Edit selected, it will auto load the setting & audio file name from device, same as Read Device button, in Device Edit mode audio file cannot be read back, can only be modify or recover.

Write Device button will download all your setting & audio files into ALM-06-WF device through Wi-Fi. Also you can copy all the file inside your project directory to the Micro SD Card.

Volume Control trackbar, range from 0(Mute)~10(Max), same as main form.

To Create new project, use Load Project button, select the directory where you want to put and add the new directory name, show as below.

Figure 3-4: New Project in Audio Editor.

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(2) Add Audio: Double Click on which File No. you are going to add the audio file,

max 64 files can be assign.

File No. play back, select Play Source (Audio file original location) or Play Project (Audio file in project) or Play Device (Audio file in ALM-06-WF device’s SD Card, only when Device Edit selected), click File No. and press Play button to play, and Stop button to break playback. Click File No. and press the Delete button to remove file name in list, show as below.

Figure 3-5: Play Back & Delete File.

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(3) Alarm Config: Frist you need to select Alarm Mode, then you can assign audio File No. for each alarm channel from combo box, playback Repeat count & Alarm Output Relay.

To simulation the alarm channel audio playback, select the channel from combo box, press Channel test button to play, and Stop to break the playback, show as below.

Figure 3-6: Alarm Config Mode0~3 & Test Input.

Figure 3-7: Alarm Config Mode4~7 & Test Input.

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3.4.1 Make a Micro SD from project

Copy all the file to the MicroSD root directory where your project directory locate,

this will be the same as Write Device from project.

3.4.2

To start a new MicroSD, please insert to a PC before use it, this will make Microsoft OS fill the

correct capacity into the MicroSD.

Insert a New MicroSD

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3.5 Alarm Mode Description

Mode 0: Channel Trigger-General Playback

 DI1 to DI6 playback in single independence trigger of 6 channels.  A pulse input triggered the Playback. Playback repeat when the input is not release.

 When alarm in playback process, any input trigger will ignore.

 The highest DIx channel priority input will take place after the previous playback complete.

Figure 3-8: ALM-06-WF Mode 0

Mode 1: Channel Trigger-Trigger Input priority Playback

 DI1 to DI6 playback in single independence trigger of 6 channels.  When alarm in playback process, any trigger input will break & take place the previous

playback.

 In this mode, it only playback once, even the input is not release.  Only when multi trigger in same time the highest DIx channel priority will take place

Figure 3-7: ALM-06-WF Mode 1

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Mode 2: Channel Trigger- Hold Repeat Playback

 DI1 to DI6 playback in single independence trigger of 6 channels.  When alarm in playback process, only higher DIx channel priority can break & take place the

previous playback.

 Playback will repeat when input are not release & will stop immediately when input released.  When multi trigger in same time the highest DIx channel priority will take place

Figure 3-6: ALM-06-WF Mode 2

Mode 3: Channel Trigger- Memory Once Playback

 DI1 to DI6 playback in single independence trigger of 6 channels.  When alarm in playback process, any trigger input will memory once for next playback.

 In this mode, it only playback once, even the input is not release.  When multi trigger in same time the highest DIx channel priority will take place

Figure 3-7: ALM-06-WF Mode 3

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Mode 4: Binary Trigger-General Playback

 DI1 to DI5 are used as binary input, max 31 channels & DI6 in single channel.  A pulse input triggered the Playback. Playback repeat when the input is not release.

 When alarm in playback process, any input trigger will ignore.

 The highest binary channel priority input will take place after the previous playback complete,

DI6 is the most highest channel.

Figure 3-8: ALM-06-WF Mode 4

Mode 5: Binary Trigger-Trigger Input priority Playback

 DI1 to DI5 are used as binary input, max 31 channels & DI6 in single channel.  When alarm in playback process, any trigger input will break & take place the previous

playback.

 In this mode, it only playback once, even the input is not release.

 The priority depend on trigger input, only when multi trigger in same time the highest binary

channel priority will take place, DI6 is the most highest channel.

Figure 3-9: ALM-06-WF Mode 5

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Mode 6: Binary Trigger- Hold Repeat Playback

 DI1 to DI5 are used as binary input, max 31 channels & DI6 in single channel.  When alarm in playback process, only highest binary channel priority can break & take place

the previous playback.

 Playback will repeat when input are not release & will stop immediately when input released.  When multi trigger in same time the highest binary channel priority will take place, DI6 is the

most highest channel.

Figure 3-10: ALM-06-WF Mode 6

Mode 7: Binary Trigger- Memory Once Playback

 DI1 to DI5 are used as binary input, max 31 channels & DI6 in single channel.  When alarm in playback process, any trigger input will memory once for next playback.

 In this mode, it only playback once, even the input is not release.

 The highest binary channel priority input will take place after the previous playback complete,

DI6 is the most highest channel.

Figure 3-11: ALM-06-WF Mode 7

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4. Application

Users can use a Computer or Smart Device to communicate with the ALM devices in

the application. It can complete the purpose of control to wireless network by this way.

Figure 4-1: ALM + PC/Laptop/Smart Device application architecture

4.1 Connection with Modbus TCP utility

a. Open Modbus TCP utility and key in the IP address , Port as "502". Finally,

click the "Connect" button.

b. If the network settings are correct, this will immediately establish a

connection.

c. Use the function code "0x02", and set the Reference Number as "0x00", Bit

Count as "0x06" to get the 6 CHs DI value.

Figure 4-2:Input Channels reading screen

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e. Use the function code "0x01", and set the Reference Number as "0x00", Bit

Count as "0x01" to get the Relay Output value.

Figure 4-3: Relay Status reading screen

g. Use the function code "0x05", and set the Reference Number as "0x00",

value as "0xFF" to turn on the Relay Output, & 0x00 to turn off.

Figure 4-4: Relay output turn On/Off

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5. Modbus Applications

The ALM-06-WF include a Modbus port that allows you to access terminals data

via Wi-Fi and communicates using a master-slave technique in which only one device (the master) can initiate transactions (called queries). The other devices (slaves) respond by supplying the requested data to the master, or by taking the action requested in the query.

Most SCADA (Supervisor Control And Data Acquisition) and HMI software can

easily integrate serial devices via the Modbus protocol, such as Citect, ICONICS, iFIX, InduSoft, Intouch, Entivity Studio, Entivity Live, Entivity VLC, Trace Mode, Wizcon, Wonderware, etc.

For Android Device, a freeware HMI Modbus is easy to use.

5.1 What is Modbus TCP/IP?

Modbus is a communication protocol developed by Modicon in 1979. Different versions of Modbus used today include Modbus RTU (based on serial

communication like RS485 and RS232), Modbus ASCII and Modbus TCP, which is the Modbus RTU protocol embedded into TCP packets.

Modbus TCP is an internet protocol. The protocol embeds a Modbus frame into a

TCP frame so that a connection oriented approach is obtained thereby making it reliable. The master query’s the slave and the slave responds with the reply. The protocol is open and hence highly scalable.

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5.2 Protocol Description

The Modbus protocol defines a simple protocol data unit independent of the

underlying communication layers. The mapping of Modbus protocol on network can

FCode

Data

(0 to 252 bytes)

introduce some additional fields on the application data unit.

Modbus/TCP Application Data Unit

Transaction ID

(2 bytes)

Protocol ID

(2 bytes)

MBAP Header Protocol Data Unit

Length

(2 bytes)

Unit ID

(1 bytes)

Figure 5-1: Modbus/TCP Application Data Unit

5.2.1 MBAP

The Modbus/TCP extension includes 7 additional bytes to the original Modbus

protocol, which allows for transport over the TCP/IP layers.

A dedicated header is used on TCP/IP to identify the Modbus Application Data

Unit. It is called the MBAP Header (MODBUS Application Protocol Header). The MBAP Header consists of 7 bytes of information:

Fields

Transaction Identifier 2 bytes

Protocol Identifier 2 bytes 0 = Modbus protocol

Length 2 bytes Number of following bytes - Includes the Unit Identifier

Unit Identifier 1 byte Identification of remote slave

Length Description

Identification of Request/Response transaction – Copied

from request to response

Table 5-1: MODBUS Application Protocol Header

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5.2.2 Function Code

The function code field of a Modbus data unit is coded in one byte. Valid codes are

in the range of 1 ... 255 decimal (the range 128 - 255 is reserved and used or exception responses). When a Modbus request is sent from a Modbus Client to a Server device the function code field tells the Server what kind of action to perform.

The Modbus/TCP feature of ALM series controller supports 6 function codes,

which allows the reading and writing of data contents of registers.

Function Code Descriptions

01 (0x01) Read Coil Status

02 (0x02) Read Input Status

03 (0x03) Read multiple Analog Output registers

05 (0x05) Force Single Coil

06 (0x06) Write single Analog Output registers register

16 (0x10) Write multiple Analog Output registers register

Table 5-2: Supports Function Codes of ALM series

Any other function code request will be returned with an error response indicating

the function code is not supported, as well as a request for too much data or data at a register address that not present.

5.2.3 Data

The data field of Modbus request sent from a client to server devices contains

additional information that the server uses to take the action defined by the function code. This can include items like discrete and register addresses, the quantity of items to be handled, and the count of actual data bytes in the field.

The data field may be nonexistent (of zero length) in certain kinds of requests, in

this case the server does not require any additional information. The function code alone specifies the action.

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5.2.4 Response

If no error occurs related to the Modbus function requested in a properly received

Modbus PDU (Protocol Data Unit) the data field of a Modbus response from a server to a client contains the data requested. If an error related to the Modbus function requested occurs, the field contains an exception code that the server application can use to determine the next action to be taken.

For example a client can read the ON/OFF states of a group of digital input or

output or it can read/write the data contents of a group of registers.

When the server responds to the client, it uses the function code field to indicate

either a normal response or that some kind of error occurred (called an exception response). For a normal response, the server simply echoes to the request the original function code.

For an exception response, the server returns a code that is equivalent to the

original function code from the request PDU with its most significant bit set to logic 1.

5.2.5 Data Encoding

Modbus uses a “big-endian” representation for address and data items. This means

that when a numerical quantity larger than single byte is transmitted, the most significant byte (MSB, also called the high-order byte) is send first. The following subtopics describe the different byte of encoding and show how the data is encoded as it is within the Modbus/TCP packet.

5.2.5.1 Binary

A binary item is represented as a single bit within a data word. All binary is packed

into 16-bits data words, which are accessed using function code 01 and 02. Therefore, a single register contains 16 bits of binary data, each having a specific meaning.

Value 1st 2nd

0xAA55

(1010101001010101)

0xAA

(10101010)

0x55

(01010101)

Table 5-3: A single register contains 16 bits of binary data

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5.2.5.2 16-bits Word

A 16-bits word item is transmitted with the most significant byte first. Function

code 03 and 04 read 16-bits items at a time; therefore, each of these data items will fit within one register that is read.

Value 1st 2nd

0x1234 0x12 0x34

Table 5-4: A 16-bits word item

5.2.5.3 32-bits Double Word

A 32-bits word item is transmitted with the most significant byte first. Function 04

read 32-bits items at a time; therefore, each of these data items will fit within 2 register that is read.

Value 1st Word 2nd Word

0x12345678 0x5678 0x1234

Table 5-5: A 32-bits double word item

5.3 ALM-06-WF Address Mapping