FieldServer FS-8700-08 - Manual (Page 3)

FS-8700-01 Modbus RTU/ASCIIFS-8700-01_Modbus_RTU.doc Driver Manual Page 3 of 21
FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web: www.fieldserver.com
Tel: (408) 262 2299 Fax: (408) 262 2269 Toll Free: (888) 509 1970 email: [email protected]
1 MODBUS RTU/ MODBUS ASCII DESCRIPTION
The Modbus RTU and Modbus ASCII drivers allow the FieldServer to transfer data to and from devices using
Modbus RTU or Modbus ASCII protocol respectively. Data can be transferred over either RS-232 or RS-485. 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.
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
1
2.2 Provided by Supplier of 3 rd Party Equipment
PART # Description
Modbus RTU or Modbus ASCII device
1 This cable is necessary for connection to the driver. It is shipped with the FieldServer and not separately with the driver.