Micromod MOD: Modcell 2050R MODBUS Communications - Manual (Page 5)

IB-23C650M
INTRODUCTION
INTRODUCTION
About This Supplement
This supplement provides instructions for installation, setup, and use of
the Modbus RS-485 serial communications option available in the
MODCELL 2050 Single Loop Controller. Comprehensive instructions
covering all aspects of the controller not related to Modbus
communication are included in the
IB-23C650 User’s Guide.
Specific information provided in this supplement is as follows:
• Instructions for connecting the controller to a Modbus network using
either a 2-Wire or 4-wire configuration.
• Application information including controller operation as a supervisory
station or computer auto/manual station using Modbus
communications.
• Step-by-step instructions for setup of the communications function
using the RS-485 MENU in the controller data base.
• Operating instructions for the controller when Modbus
communication with a host device is enabled.
• A description of the Modbus messages supported and the message
formats.
• Controller attribute reference data. The listing includes register data
for numeric attributes and coil data for boolean (discrete) attributes.
About Modbus Communications
A 2050R controller and a host device connected to a Modbus network
communicate via a master/slave relationship. The host device functions
as the Modbus master and the controller functions as the slave. The
master is in command of the communications transaction and talks to
one slave (controller) at a time. The master sends a message to a
slave and waits to receive an answer back from that slave before it
talks to the another slave. Each slave has a unique address which
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