FieldServer FS-8700-01 Modbus RTU, FS-8700-08 Modbus ASCII Instruction Manual

A Sierra Monitor Company

Driver Manual

(Supplement to the FieldServer Instruction Manual)

FS-8700-01 Modbus RTU

&

FS-8700-08 Modbus ASCII

There are several similarities between these two drivers and

we have incorporated them into the same manual to ensure

that our information stays current. Although both drivers

are referenced in this manual, they are different drivers and

need to be ordered separately."

APPLICABILITY & EFFECTIVITY

Effective for all systems manufactured after May 1, 2001

Instruction Manual Part Number: T28700-01

Rev. A.

Applicability and Effectivity

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Table of Contents

Table of Contents

1. Modbus RTU/ Modbus ASCII Description ....................................................................... 3

2. Driver Scope of Supply..................................................................................................... 4

2.1. Supplied by FieldServer Technologies for this driver.................................................... 4

2.2. Provided by Supplier of 3rd Party Equipment................................................................ 4

3. Hardware Connections ..................................................................................................... 5

4. Configuring the FieldServer as a Modbus RTU or Modbus ASCII Client. ..................... 6

4.1. Data Arrays/Descriptors............................................................................................... 6

4.2. Client Side Connection Descriptors.............................................................................. 7

4.3. Client Side Node Descriptors ....................................................................................... 8

4.4. Client Side Map Descriptors......................................................................................... 9

4.4.1. FieldServer Related Map Descriptor Parameters.................................................. 9

4.4.2. Driver Related Map Descriptor Parameters........................................................... 9

4.4.3. Timing Parameters................................................................................................ 9

4.4.4. Map Descriptor Examples....................................................................................10

5. Configuring the FieldServer as a Modbus RTU or Modbus ASCII Server....................11

5.1. Server Side Connection Descriptors ...........................................................................11

5.2. Server Side Node Descriptors.....................................................................................12

5.3. Server Side Map Descriptors ......................................................................................13

5.3.1. FieldServer Specific Map Descriptor Parameters.................................................13

5.3.2. Driver Specific Map Descriptor Parameters .........................................................13

5.3.3. Map Descriptor Examples....................................................................................14

Appendix A. Advanced Topics – Modbus RTU..................................................................15

Appendix A.1. Data Types ..................................................................................................15

Appendix A.2. Single Writes................................................................................................16

Appendix A.3. Read/write Operation ...................................................................................16

Appendix A.4. Managing Floating points with Modbus ........................................................17

Appendix A.5. Connection to York Modbus Microgateway ..................................................18

Appendix A.6. Node_Offline_Response..............................................................................19

Appendix B. Modbus ASCII - Examples of FieldServer setup for typical clients ............20

Appendix B.1. FieldServer with GE Cimplicity as client .......................................................20

Appendix B.2. FieldServer with Intellution FIX as a client....................................................20

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 3 of 21

1. Modbus RTU/ Modbus ASCII Description

The Modbus RTU and Modbus ASCII drivers allow the FieldServer to transfer data to and from
devices over either RS-232 or RS-485 using Modbus RTU or Modbus ASCII protocol
respectively. The driver was developed for Modbus Application Protocol Specification V1.1a"
from Modbus-IDA. The specification can be found at www.modbus.org. The FieldServer can
emulate either a Server or Client.

The information that follows describes how to expand upon the factory defaults provided in the
configuration files included with the FieldServer.

There are various register mapping models being followed by various vendors
To cover all these models FieldServer uses the following three Models

• Modicon_5digit – Use this format where addresses are defined in 0xxxx, 1xxxx, 3xxxx or
4xxxx format. A maximum of 9999 registers can be mapped of each type. This is
FieldServer driver’s default format.

• ADU –Application Data Unit address. Use this format where addresses of each type are
defined in the range 1-65536

• PDU –Protocol Data unit address. Use this format where addresses of each type are
defined in the range 0-65535.

The key difference between ADU and PDU is for example if Address_Type is ADU and address
is 1, the driver will poll for register 0. If Address_Type is PDU, the driver will poll for address 1.

Note 1: If vendor document shows addresses in extended Modicon (i.e. 6 digit) format like
4xxxxx then consider these addresses as xxxxx (omit the first digit) and use either ADU or PDU

Note 2: The purpose of providing 3 different ways of addressing the Modbus registers is to allow
the user to choose the addressing system most compatible with the address list being used. At
the protocol level, the same protocol specification is used for all three with the exception of the
limited address range for Modicon_5digit.

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 4 of 21

2. Driver Scope of Supply

2.1. Supplied by FieldServer Technologies for this driver

FIELDSERVER TECHNOLOGIES PART # DESCRIPTION

FS-8915-10 UTP cable (7 foot) for RS-232 use
FS-8917-02 RJ45 to DB9F connector adapter
FS-8917-01 RJ45 to DB25M connection adapter
FS-8917-21 RS-485 connection adapter
FS-8700-01 (T28700-01) Driver Manual

2.2. Provided by Supplier of 3rd Party Equipment

PART # DESCRIPTION

Modbus RTU or Modbus ASCII device

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 5 of 21

3. Hardware Connections

It is possible to connect a Modbus RTU or Modbus ASCII device to any of the existing serial
ports on the FieldServer1. These ports simply need to be configured for the appropriate driver in
the configuration file.

Configure the Modbus RTU or Modbus ASCII device according to manufacturer’s instructions.

1

Not all ports shown are necessarily supported by the hardware. Consult the appropriate Instruction

manual for details of the ports available on specific hardware.

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 6 of 21

4. Configuring the FieldServer as a Modbus RTU or Modbus ASCII Client.

For a detailed discussion on FieldServer configuration, please refer to the FieldServer
Configuration Manual. The information that follows describes how to expand upon the factory
defaults provided in the configuration files included with the FieldServer (See “.csv” sample files
provided with the FieldServer).

This section documents and describes the parameters necessary for configuring the FieldServer
to communicate with a Modbus RTU or Modbus ASCII Server.

4.1. Data Arrays/Descriptors

The configuration file tells the FieldServer about its interfaces, and the routing of data
required. In order to enable the FieldServer for Modbus RTU or Modbus ASCII
communications, the driver independent FieldServer buffers need to be declared in the
“Data Arrays” section, the destination device addresses need to be declared in the “Client
Side Nodes” section, and the data required from the Servers needs to be mapped in the
“Client Side Map Descriptors” section. Details on how to do this can be found below.

Note that in the tables, * indicates an optional parameter, with the bold legal value being the
default.

Section Title

Data_Arrays

Column Title Function Legal Values

Data_Array_Name Provide name for Data Array

Provide data format. Each

Data_Array_Format

Data Array can only take on
one format.
Number of Data Objects. Must
be larger than the data

Data_Array_Length

storage area required by the
map descriptors for the data
being placed in this array.

Example

// Data Arrays
Data_Arrays
Data_Array_Name, Data_Array_Format, Data_Array_Length
DA_AI_01, UInt16, 200
DA_AO_01, UInt16, 200
DA_DI_01, Bit, 200
DA_DO_01, Bit, 200

Up to 15 alphanumeric
characters
FLOAT, BIT, UInt16, SInt16,
Packed_Bit, Byte,
Packed_Byte, Swapped_Byte

1-10,000

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 7 of 21

4.2. Client Side Connection Descriptors

Section Title

Connections

Column Title Function Legal Values

Port

Baud* Specify baud rate

Parity* Specify parity
Data_Bits*

Stop_Bits*

Protocol

Handshaking* Handshaking is not supported
Poll Delay*

Example

Change protocol to MB_ASCII to use Modbus ASCII protocol

// Client Side Connections

Connections
Port, Baud, Parity, Data_Bits, Stop_Bits, Protocol, Handshaking, Poll_Delay
P8, 9600, None, 8, 1, Modbus _RTU, None, 0.100s

Specify which port the device is
connected to the FieldServer

Specify data bits
Specify stop bits

Specify protocol used

Time between internal polls

P1-P8, R1-R22

110 – 115200, standard baud
rates only. 9600
Even, Odd, None

7, 8
1 (Vendor limitation)

Modbus RTU
Modbus _RTU
Modbus ASCII
MB_ASCII

None

0-32000s, 0.05s

2

Not all ports shown are necessarily supported by the hardware. Consult the appropriate Instruction

manual for details of the ports available on specific hardware.

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 8 of 21

4.3. Client Side Node Descriptors

Section Title

Nodes

Column Title Function Legal Values

Node_Name Provide name for Node

Node_ID

Modbus station address of physical
Server Node

Protocol Specify protocol used

Port

Specify which port the device is
connected to the FieldServer
Set to Block_Mode if Remote Server

Node_Type3

Node (RSN) only supports Write
Multiple – FC16 & FC15, and does
not support FC05 or FC06

Address_Type

4

Specify Register Mapping Model

Example:

Change protocol to MB_ASCII to use Modbus ASCII protocol

// Client Side Nodes
// For devices where 65536 addresses are available in each memory area.
Nodes
Node_Name, Node_ID, Protocol, Port Address_Type
Modbus device 1, 1, Modbus_RTU, P8 ADU
Modbus device 2, 2, Modbus_RTU, P8 PDU
// For devices where only 9999 registers are available in each memory area.
Nodes
Node_Name, Node_ID, Protocol, Port
Modbus device 3, 3, Modbus_RTU, P8

Up to 32 alphanumeric
characters

1-255

Modbus RTU
Modbus_RTU
Modbus ASCII
MB_ASCII

P1-P8, R1-R2

2

Block_Mode

ADU,PDU, -, Modicon_5digit

3

If this parameter is not specified the default function codes will be FC 05 (Single_Coil) and FC 06

(Single_Register). Refer to Appendix A.3 for more information.

4

Optional for Modicon 5 digit devices

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 9 of 21

4.4. Client Side Map Descriptors

4.4.1. FieldServer Related Map Descriptor Parameters

Column Title Function Legal Values

Map_Descriptor_Name Name of this Map Descriptor

Data_Array_Name

Data_Array_Offset Starting location in Data Array

Function Function of Client Map Descriptor RDBC, WRBC, WRBX

Name of Data Array where data
is to be stored in the FieldServer

Up to 32 alphanumeric
characters
One of the Data Array names
from “Data Array” section above
0 to maximum specified in “Data
Array” section above

4.4.2. Driver Related Map Descriptor Parameters

Column Title Function Legal Values

Node_Name

Data_Type5

Address

Length

Data_Array_Low_Scale*

Data_Array_High_Scale*

Node_Low_Scale*

Node_High_Scale*

Name of Node to
fetch data from

Specify memory
area

Starting address of
read block

Length of Map
Descriptor
Scaling zero in
Data Array

Scaling max in Data
Array

Scaling zero in
Connected Node
Scaling max in
Connected Node

One of the Node names specified in “Client
Node Descriptor” above
Address_Type = ADU
Coil, Discrete_Input, Input_Register,
Holding_Register, Single_Coil,
Single_Register
Address_Type = PDU
FC01, FC02, FC03, FC04,
FC05, FC06, FC15, FC16
Address_Type = Modicon_5digit

- (Dash), Single_Register, Single_Coil
Address_Type = ADU
1-65536
Address_Type = PDU
0-65535
Address_Type = Modicon_5digit
40001, 30001, etc
1-125 (For Analog polls),
1-800 (For Binary polls).

Any signed 32 bit integer in the range:

-2,147,483,648 to 2,147,483,647. 0

Any signed 32 bit integer in the range:

-2,147,483,648 to 2,147,483,647. 100
Any signed 32 bit integer in the range:

-2,147,483,648 to 2,147,483,647. 0
Any signed 32 bit integer in the range:

-2,147,483,648 to 2,147,483,647. 100

4.4.3. Timing Parameters

Column Title Function Legal Values

Scan_Interval* Rate at which data is polled

5

Optional only for Modicon_5digit addressing, and only if Single writes do not need to be forced

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

0-32000, 1

4.4.4. Map Descriptor Examples.

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 10 of 21

// Client Side Map Descriptors

// Note: All three examples below are addressing the same Modbus registers.

// For Nodes where Address_Type is ADU

Map_Descriptors

Map_Descriptor_Name, Data_Array_Name, Data_Array_Offset, Function, Node_Name, Data_Type, Address, Length, Scan_Interval

CMD_AI_01, DA_AI_01, 0, RDBC, MODBUS DEVICE1, Input_Register, 1, 20, 1.000s

CMD_AO_01, DA_AO_01, 0, RDBC, MODBUS DEVICE1, Holding_Register, 1, 20, 1.000s

CMD_DI_01, DA_DI_01, 0, RDBC, MODBUS DEVICE1, Discrete_Input, 1, 20, 1.000s

CMD_DO_01, DA_DO_01, 0, RDBC, MODBUS DEVICE1, Coil, 1, 20, 1.000s

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

// For Nodes where Address_Type is PDU

Map_Descriptors

Map_Descriptor_Name, Data_Array_Name, Data_Array_Offset, Function, Node_Name, Data_Type, Address, Length, Scan_Interval

CMD_AI_02, DA_AI_02, 0, RDBC, MODBUS DEVICE2, FC04, 0, 20, 1.000s

CMD_AO_02, DA_AO_02, 0, RDBC, MODBUS DEVICE2, FC03, 0, 20, 1.000s

CMD_DI_02, DA_DI_02, 0, RDBC, MODBUS DEVICE2, FC02, 0, 20, 1.000s

CMD_DO_02, DA_DO_02, 0, RDBC, MODBUS DEVICE2, FC01, 0 20, 1.000s

// For Nodes where Address_Type is Modicon_5digit.

Map_Descriptors

Map_Descriptor_Name, Data_Array_Name, Data_Array_Offset, Function, Node_Name, Address, Length, Scan_Interval

CMD_AI_03, DA_AI_03, 0, RDBC, MODBUS DEVICE3, 30001, 20, 1.000s

CMD_AO_03, DA_AO_03, 0, RDBC, MODBUS DEVICE3, 40001, 20, 1.000s

CMD_DI_03, DA_DI_03, 0, RDBC, MODBUS DEVICE3, 10001, 20, 1.000s

CMD_DO_03, DA_DO_03, 0, RDBC, MODBUS DEVICE3, 00001, 20, 1.000s

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 11 of 21

5. Configuring the FieldServer as a Modbus RTU or Modbus ASCII Server

For a detailed discussion on FieldServer configuration, please refer to the FieldServer
Configuration Manual. The information that follows describes how to expand upon the factory
defaults provided in the configuration files included with the FieldServer (See “.csv” sample files
provided with the FieldServer).

This section documents and describes the parameters necessary for configuring the FieldServer
to communicate with a Modbus RTU or Modbus ASCII Client.

The configuration file tells the FieldServer about its interfaces, and the routing of data required.
In order to enable the FieldServer for Modbus RTU or Modbus ASCII communications, the
driver independent FieldServer buffers need to be declared in the “Data Arrays” section, the
FieldServer virtual Node(s) needs to be declared in the “Server Side Nodes” section, and the
data to be provided to the clients needs to be mapped in the “Server Side Map Descriptors”
section. Details on how to do this can be found below.

Note that in the tables, * indicates an optional parameter, with the bold legal value being the
default.

5.1. Server Side Connection Descriptors

Section Title

Connections

Column Title Function Legal Values

Port

Baud* Specify baud rate

Parity* Specify parity Even, Odd, None
Data_Bits*

Stop_Bits*

Protocol

Handshaking* Handshaking is not supported.

Example

Change protocol to MB_ASCII to use Modbus ASCII protocol
// Server Side Connections

Connections
Port, Baud, Parity, Data_Bits, Stop_Bits, Protocol, Handshaking
P1, 9600, None, 8, 1, Modbus_RTU, None

Specify which port the device is connected
to the FieldServer

Specify data bits
Specify stop bits

Specify protocol used

P1-P8, R1-R26

110 – 115200, standard baud
rates only

7, 8
1 (Vendor limitation)

Modbus RTU
Modbus_RTU
Modbus ASCII
MB_ASCII
None

6

Not all ports shown are necessarily supported by the hardware. Consult the appropriate Instruction

manual for details of the ports available on specific hardware.

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 12 of 21

5.2. Server Side Node Descriptors

Section Title

Nodes

Column Title Function Legal Values

Node_Name Provide name for Node Up to 32 alphanumeric characters
Node_ID Node ID of physical Server Node 1 – 255
Protocol Specify protocol used Modbus RTU
Address_Type7 Specify Register Mapping Model

Example

Change protocol to MB_ASCII to use Modbus ASCII protocol

// Server Side Nodes
// For devices where 65536 addresses are available in each memory area.
Nodes
Node_Name, Node_ID, Protocol Address_Type
MB_Srv_11, 11, Modbus_RTU ADU
MB_Srv_12, 12, Modbus_RTU PDU
// For devices where only 9999 registers are available in each memory area.
Nodes
MB_Srv_13, 13, Modbus_RTU
MB_Srv_14, 14, Modbus_RTU -

ADU,PDU, -, Modicon_5digit

Modicon_5digit

7

Optional for Modicon 5 digit devices

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 13 of 21

5.3. Server Side Map Descriptors

5.3.1. FieldServer Specific Map Descriptor Parameters

Column Title Function Legal Values

Map_Descriptor_Name Name of this Map Descriptor

Data_Array_Name

Data_Array_Offset Starting location in Data Array

Function

Name of Data Array where data
is to be stored in the FieldServer

Function of Server Map
Descriptor

Up to 32 alphanumeric
characters
One of the Data Array names
from “Data Array” section above
0 to maximum specified in “Data
Array” section above

Server

5.3.2. Driver Specific Map Descriptor Parameters

Column Title Function Legal Values

Node_Name

Data_Type8 Specify memory area

Length

Address

Data_Array_Low_Scale*

Data_Array_High_Scale*

Node_Low_Scale*

Node_High_Scale*

Node_Offline_Response

Name of Node to fetch
data from

Length of Map
Descriptor

Starting address of
read block

Scaling zero in Data
Array
Scaling max in Data
Array
Scaling zero in
Connected Node
Scaling max in
Connected Node
Set the FieldServer
response to the
Modbus RTU Client
when the Server Node
supplying the data has
gone offline

One of the Node names specified in
“Client Node Descriptor” above
Address_Type = ADU
Coil, Discrete_Input, Input_Register,
Holding_Register, Single_Coil,
Single_Register
Address_Type = PDU
FC01, FC02, FC03, FC04,
FC05, FC06, FC15, FC16
Address_Type = Modicon_5digit

- (Dash), Single_Register, Single_Coil

1-10000.

Address_Type = ADU
1-65536
Address_Type = PDU
0-65535
Address_Type = Modicon_5digit
40001, 30001, etc

Any signed 32 bit integer in the range:

-2,147,483,648 to 2,147,483,647. 0
Any signed 32 bit integer in the range:

-2,147,483,648 to 2,147,483,647. 100
Any signed 32 bit integer in the range:

-2,147,483,648 to 2,147,483,647. 0
Any signed 32 bit integer in the range:

-2,147,483,648 to 2,147,483,647. 100
No_Response,
Old_Data,
Zero_Data,
FFFF_Data,
Refer to Appendix A.6 for further
information.

8

Optional only for Modicon_5digit addressing, and only if Single writes do not need to be forced

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

5.3.3. Map Descriptor Examples

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 14 of 21

// Server Side Map Descriptors where Node Address_Type is ADU

// Note: All three examples below are addressing the same Modbus registers. // For Nodes where Address_Type is ADU

Map_Descriptors

Map_Descriptor_Name Data_Array_Name Data_Array_Offset, Function Node_name, Data_type Address, Length, Data_Array_Low_Scale, Data_Array_High_Scale Node_Low_Scale Node_High_Scale

SMD_AI_01, DA_AI_01, 0, Server, MB_Srv_11 Input_Register 1, 200, 0, 100, 0, 10000

SMD_AO_01, DA_AO_01, 0, Server, MB_srv_11 Holding_Register 1, 200, 0, 100, 0, 10000

// Server Side Map Descriptors where Node Address_Type is PDU

Map_Descriptors

Map_Descriptor_Name Data_Array_Name Data_Array_Offset, Function Node_name, Data_type Address, Length, Data_Array_Low_Scale, Data_Array_High_Scale Node_Low_Scale Node_High_Scale

SMD_AI_02, DA_AI_02, 0, Server, MB_Srv_12 FC04 0, 200, 0, 100, 0, 10000

SMD_AO_02, DA_AO_02, 0, Server, MB_srv_12 FC03 0, 200, 0, 100, 0, 10000

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

// For Nodes where Address_Type is Modicon_5digit.

Map_Descriptors

Map_Descriptor_Name, Data_Array_Name, Data_Array_Offset, Function, Node_name, Address, Length, Data_Array_Low_Scale, Data_Array_High_Scale Node_Low_Scale Node_High_Scale

SMD_AI_01, DA_AI_01, 0, Server, MBP_Srv_13, 30001, 200, 0, 100, 0, 10000

SMD_AO_01, DA_AO_01, 0, Server, MBP_Srv_13, 40001, 200, 0, 100, 0, 10000

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 15 of 21

Appendix A. Advanced Topics – Modbus RTU

Appendix A.1. Data Types

If Node parameter Address_Type is set as ADU or PDU, then Data_Type must be specified
as follows
For Address_Type ADU :

Address range Data_Type Function Code (Write) Function Code (Read)

1 - 65536 Coil 15 1
1 – 65536 Discrete_Input n/a. 2
1 – 65536 Input_Register n/a. 4
1 - 65536 Holding_Register 16 3

For Address_Type PDU :

Address range Data_Type Function Code (Write) Function Code (Read)

0 - 65535 FC01 15 1
0 – 65535 FC02 n/a. 2
0 – 65535 FC04 n/a. 4
0 – 65535 FC03 16 3

For Address_Type Modicon_5digit
When a Modbus address range is specified, a particular Data Type is implied. The defaults
are as follows:

Address range Data_Type Function Code (Write) Function Code (Read)

40001 - 49999 Register 16 3
30001 - 39999 Analog _Input n/a. 4
10001 - 19999 Digital_Input n/a. 2
00001 - 09999 Coil 15 1

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 16 of 21

Appendix A.2. Single Writes

For pure write operations where the function = WRBC or WRBX, the driver defaults to using
Function Codes 15 and 16 (Multiple writes). It is possible to force the driver to use Function
Codes 5 and 6 (Single Writes) by manipulating the Data_Type parameter as follows:

For Address_Type ADU:

Address range Data_Type Function Code (Write)

1 - 65536 Single_Coil 5
1 - 65536 Single_Register l 6

For Address_Type PDU:

Address range Data_Type Function Code (Write)

0 - 65535 FC05 5
0 - 65535 FC06 6

For Address_Type Modicon_5digit

Address range Data_Type Function Code (Write)

40001 - 49999 Single_Register 6
30001 - 39999 Single_Coil 5.

Example: FC 6 = Write Single Register

Add a parameter to the Modbus client side Map Descriptor called Data_Type.
If you specify the Data_Type as Single_Register and the Function as WRBC or WRBX,
then a Modbus poll with FC 6 will be generated.
Logically Single Register implies a length of one, and even if you try to set the length longer
in the csv file, the length is limited to 1 in the driver.

Appendix A.3. Read/write Operation

When using the driver as a Modbus master, the function RDBC allows read/write capability
with Register and Coil data types. If defaults are used, then Function codes 5 and 6 (Single
Writes) are used to write data back to the registers being read, regardless of data length
being read. If multiple writes (FC 15 and 16) are needed for Read/write operation, the user
needs to specify the Node_Type parameter in the Client Side Nodes Section and set it to
Block_Mode.

Note that block writes of length 1 are currently all that is supported.

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

Appendix A.4. Managing Floating points with Modbus

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 17 of 21

Modbus as a standard does not support floating point formats. Many vendors have written higher level communications software to

use two 16 bit registers to represent floating point or 32 bit integers. This requires conversion software on both ends of the

communication channel. The FieldServer supports this function and also provides other options to resolve this issue.

Transferring non-integer values with one register

It is possible to represent values higher than 32767 using one register in one of two ways:

• Declare data arrays as type Uint16 (Unsigned integer). This will give you a range from 0 to 65535.

• Use the scaling function on the FieldServer, which will allow you to set up any range, with 16 bit resolution.

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Map_Descriptors

Map_Descriptor_Name, Data_Array_Name, Data_Array_Offset, Function, Node_Name, Address, Length, Data_Array_Low_Scale, Data_Array_High_Scale, Node_Low_Scale, Node_High_Scale,

SMD_AI1, DA_AI_01, 0, Server, MBP_Srv_11, 30001, 200, 0, 100, 0, 10000

SMD_AO1, DA_AO_01, 0, Server, MBP_Srv_11, 40001, 200, 0, 100, 0, 10000

This example multiplies the values in the data array by 100 (10000 on Node_High_Scale is 100X larger than 100 on

Data_Array_High_Scale). This is most commonly used when the user wants to introduce values after the decimal point. For

example, a value of 75.6 will be sent as 7560, which can then be rescaled by the Modbus master.

The following example shows how scaling can be achieved on the Server side of the configuration. Note that scaling can also be

done on the Client side to scale down a value that was scaled up by a Modbus vendor. Further information regarding scaling can be

found in the FieldServer Configuration manual.

Example :

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 18 of 21

Modbus

Special

Transferring 32 bit values with two registers

If a Modbus Server sends two consecutive registers to the FieldServer representing either a
floating point value or a 32 bit integer value, the FieldServer can combine and decode these
registers back into their original format. To do this, the user must read the registers into an
integer data array, and then use the Moves function to move the data to a floating point or
32 bit integer data array. The “function” field in the move must be populated with the correct
move function required. Details of the available function fields are listed in the FieldServer
configuration manual along with a more detailed explanation of moves. Note that functions
also exist to split a floating point value into two integers using the reverse operation.

A diagrammatic representation of this process is depicted below:

Modbus
Device

Two 16 bit
integers
polled:
e.g: 40001,
length 2
Together, they
combine to
form a 32 bit
IEEE Floating
point number.

Source Data
Array

------------------------­Offset 0: 40001

------------------------­Offset 1: 40002

-------------------------

Move

Float Data Array

------------------------­Offset 40: Float value

-------------------------

Sensible data

Unreadable

content

The example below shows how a floating point value is retrieved from two Modbus registers
that were placed in an integer data array.

Example

Data_Arrays
Data_Array_Name, Data_Format, Data_Array_Length
DA1, int16, 20
DA2, float, 10

Moves
Function, Source_Data_Array, Source_Offset, Target_Data_Array, Target_Offset

2.i16-1.float-sw, DA1, 0, DA2, 6

This Move will cause two integers at offsets 0 and 1 in the integer Data Array DA1 to be
copied to offset 6 in the float Data Array DA2. In the process of copying the values, the
integers will be combined and treated as an IEEE 32 bit floating point number.

Appendix A.5. Connection to York Modbus Microgateway

If connecting the FieldServer to a York Modbus Microgateway, the Node_ID of the
Microgateway is defined by the address DIP switches. If switch 4 is set to ‘On’ and the other
switches are set to ‘off’ then Node_ID of the Microgateway is ‘247’, the parity is ‘Even’, and
the stop bits are 1. Other Node_ID combinations can be found in the York Modbus
Microgateway Installation Manual.

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 19 of 21

Appendix A.6. Node_Offline_Response

This function is specific to the Modbus RTU driver.

In systems where data is being collected from multiple Server Nodes and made available on
a FieldServer configured as a Modbus RTU Server, when a Server Node goes offline the
default behavior of the FieldServer would be to stop responding to polls for this data. This
might not be what the user wants. Various options exist making it possible to signal that the
data quality has gone bad without creating error conditions in systems sensitive to the
default option.

The following options can be configured under the Node parameter,
Node_Offline_Response, to set the response of the FieldServer to the Modbus RTU Client
when the Server Node supplying the data is offline:

• No_Response - this is the default option. The FieldServer simply does not respond when

the corresponding Server Node is offline.

• Old_Data - The FieldServer will respond, but with the last known value of the data. This

maintains the communication link in an active state, but may hide the fact that the Server
Node is offline.

• Zero_Data - The FieldServer will respond, but with the data values set to zero. If the

user normally expects non-zero values, this option will signal the offline condition without
disrupting communications.

• FFFF_Data - The FieldServer will respond, but with the data values set to FFFF (hex). If

the user normally expects other values, this option will signal the offline condition without
disrupting communications.

Example:

Nodes
Node_name, Node_ID, Protocol, Node_Offline_Response, port
DEV11, 11, Modbus_rtu, No_Response, ­DEV12, 12, Modbus_rtu, Old_Data, ­DEV15, 15, Modbus_rtu, Zero_Data, ­DEV16, 16, Modbus_rtu, FFFF_Data, -

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 20 of 21

Appendix B. Modbus ASCII - Examples of FieldServer setup for typical clients

Appendix B.1. FieldServer with GE Cimplicity as client

• Run the Cimplicity “Workbench” and create a “New Project” with a unique “Project

Name” option of “Basic Control” and protocol “Modbus ASCII”.

• Check the project properties and continue with the “Project Wizard Setup” that appears.

• Add Modbus port giving it a description.

• Create and configure the devices, select “new item”.

• Name the device, select the port, give it a description (e.g. FieldServer), and choose

“SYSTEM” resource.

• Create and configure the points.

• Select “new item”, name the point and choose the appropriate device.

• Under the “General” tab, point properties require a description. Note that the elements

must have a value greater than 8.

• Under the “Device” tab, properties need the appropriate address (e.g. 40001 and also

require the leading 0’s), change the update criteria to “On Scan”.

• When the project is configured, run by pressing the “play” button.

• Expect the Cimplicity driver to connect and poll the FieldServer for a range of valid

addresses, and then proceed to poll for just the configured Points.

• From the start menu choose the “Point Control Panel”, select edit and add the project

you want to view. Note, to log on the User name “ADMINISTRATOR” must be supplied

• Use “Modbus ASCII Diagnostics” to connect to host and then read the register.

Appendix B.2. FieldServer with Intellution FIX as a client

• Install Intellution FIX, choosing the MB1 Modbus ASCII I/O driver

• Run from Start menu and choose “Intellution Fix”.

• Choose “System Configuration Utility”.

• Modify SCADA, add the MB1 Modbus ASCII I/O driver

• Configure the Modbus ASCII Driver.

• Device is D11, select 5-digit address, add the FieldServer virtual Node ID to station

address

• Set up poll record

• SAVE the configuration.

• Open “StaRTUp”

• Open “Mission Control” from the “Apps” menu and confirm Fix is polling.

• To display the data create a link in Fix draw, add link, data link.

• Give it a tagname, allow data entry, numeric entry and set enable option.

• If tag is not in database, select “Add”, choose “AR”. Then set output enable , device

MB1, I/O address d11.

• Save the settings

• Use “Quickview” from the “View” menu to confirm the reading of data without ???

appearing

• Change the value and wait a few seconds to ensure the change really occurred.

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]

FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 21 of 21

THIS PAGE INTENTIONALLY LEFT BLANK

FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.FieldServer.com

Tel: [phone] Fax: [phone] Toll_Free: 888-509-1970 email: [e-mail]