3-1
3
3
Programming Instructions
3.1
INTRODUCTION
This section describes the operation of the 8099 Ethernet to Modbus Interface
and how it is used to control slave Modbus devices. Because programming
the 8099 over a network is different from traditional GPIB programming, a
new user should read Appendixes A1 and A2 to familiarize himself with the
VXI-11 concepts before programming the 8099. When the client application
is linked to an 8099, the commands and operation of the Modbus Interface is
substantially identical to that of ICS's 4899A GPIB to Modbus Interface.
3.2
OPERATION
3.2.1 VXI-11 Operation
The 8099 is a server in the client-server relationship and provides a VXI-11
service. The core channel link to interface
inst0
in the 8099 is used for all
commands and responses including 488.2, SCPI and Modbus commands. The
8099 does not have any additional interface personalities. The VISA Resource
String is:
TCPIP::
ip
::inst0::INSTR where
ip
is the ip address
3.2.2 Basic Modbus Operation
The 8099 is an VXI-11.3, IEEE-488.2 compatible device and responds to three
types of commands: IEEE-488.2 Common Commands, SCPI Commands and
a set of Modbus Commands to communicate with Modbus device(s). The
IEEE-488.2 and SCPI commands are used to setup and configure the 8099's
IEEE-488.2 Status Reporting Structure and its Serial parameters. Any com-
mands that end in a ‘?’ are a query and the 8099 responds by outputting the
response to the client the next time it receives a device_read message. (similar
to a GPIB Talk address).