20
41-621.1 HART
®
to Modbus
®
Adaptor Operating Manual
7.
Basic Modbus ASCII Communication over RS-485
7.1.
Purpose
This procedure instructs how to configure the HART to Modbus Adaptor (HMA) to support the Modbus
ASCII protocol.
7.2.
Equipment
Item
Manufacturer
Model
HART to Modbus Adaptor
MII
031-2859-001
RS485 Communications cable
FDTIchip
USB-RS485-WE
Termination resistor
-
120
Modbus host application
www.modbustools.com
Modbus Poll
Power Supply
-
20-24V, 0.5A
7.3.
Setup
Connect the HMA to a power supply via the power terminal block. Connect an RS-485 communications
cable to the RS-485 terminal block of the HMA, with the Receive/Transmit Data+ A lead (orange) on
the positive terminal and the Receive/Transmit Data
–
B lead (yellow) on the negative terminal.
Connect a 120
resistor between the two RS-485 terminal block positions. Connect the other end of
the cable to a PC which has a Modbus host application.
7.4.
Procedure
7.4.1
Using Procedure 1, ensure that registers 3000 through 3007 of the HMA match the values
for the Modbus ASCII protocol settings used by the intended Modbus master. Refer to
Appendix G for the HMA Communication settings. If the settings do not match, double-
click on a value that needs to be changed in order to open the Write Single Register
dialog, enter the new value, and then click on Send.
7.4.2
Change DIP switch 1 to ON. This sets the device to run in the selected communications
mode.
7.4.3
Verify that the device is not communicating with the Modbus Poll application.
7.4.4
Select Connection\Disconnect from the Modbus Poll menu bar.
Summary of Contents for Jupiter JM4
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