Magnetrol Jupiter JM4, Operating Manual

Page: 19 / 124

41-621.1 HART ® to Modbus ® Adaptor Operating Manual
19
6.
Basic Modbus RTU Communication over RS-232
6.1.
Purpose
This procedure instructs how to configure the HART to Modbus Adaptor (HMA) to support the Modbus
protocol over RS-232.
6.2.
Equipment
Item Manufacturer Model
HART to Modbus Adaptor MII 031-2859-001
RS485 Communications cable FDTIchip USB-RS485-WE
RS232 Communications cable FDTIchip USB-RS232-WE-1800-BT_0.0
Termination resistor - 120

Modbus host application www.modbustools.com Modbus Poll
Power Supply - 20-24V, 0.5A
Level transmitter MII Model 706
Probe MII Model 706 compatible
6.3.
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.
6.4.
Procedure
6.4.1
Using Procedure 1, ensure that registers 3000 through 3007 of the HMA match the values
for the Modbus RTU protocol settings used by the intended Modbus master. Refer to
Appendix F 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.
6.4.2
Change the DIP switches 3 and 4 to 3 == ON, 4 == OFF.
6.4.3
Change DIP switch 1 to ON. This sets the device to run in the selected communications
mode.
6.4.4
Disconnect the RS-485 communication cable from the HMA.
6.4.5
Connect the HMA to a Modbus master using a RS-232 communications cable. Connect
the
master’s RS-232 TX line (orange) to the ‘ + ‘ position of the RS -485 terminal block, and
the RX line (yellow) to the ‘ - ‘ position .
6.4.6
Verify that the Modbus master is receiving responses from the HMA (Tx is increasing) and
that there are no communication errors being reported.