User`s guide

Establishing Communications
Modbus Communications
Release E UMC800 Control Builder User’s Guide 31
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Modbus Communications
Overview
An optional serial communication card is available that provides two RS485 serial communication ports.
Both ports support the Modbus RTU protocol, one functioning as a Slave, the other as a Master.
Slave Communications: The multi-drop Slave communication port may be networked with up to 31
UMC800 controllers or other Modbus compatible devices to a single PC or host device. The
communication protocol allows read and write operations to the data parameters of the controller, including
analog and digital inputs and outputs, loop parameters, calculations, setpoint programs and schedules.
Master Communications: The Master communication port supports read and write operations for up to 16
Modbus compatible devices. The data transferred via this port is integrated into the user’s control strategy
through read and write function blocks. A single function block supports reading and writing up to 4
parameters each to a slave device. Two additional blocks are available that support reading up to 16
parameters or writing up to 8 parameters. Multiple function blocks may be assigned to a single external
device. The data exchanged with external devices is limited to a 2-second maximum rate.
Set Controller Comm A Port
• If you select “Set Controller Comm A Port” in the Communications menu, the Set Up Controller
Comm A Port dialog box will appear.
Click to enable
Comm Port
Click Radio Button
to select Baud Rate
Click to select
Word/Byte order
for Floating Point
Communication Data
Enter Comm ID
number between
1 and 247
Set Controller Comm B Port
• If you select “Set Controller Comm B Port” in the Communications menu, the Set Up Controller
Comm B Port dialog box will appear.
Click radio button
to select Baud Rate.