Siemens DTU3005-B Operator's Manual page 35

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Select either ASCII or RTU as your Modbus protocol,
then press the Tab key to highlight the Modbus ID
selection box. The Modbus ID is used to identify the
address of the DTU. Type in the Modbus ID number
and press Enter.
2-Wire RS422 or RS485 Communications
After you have entered the Modbus ID number, high-
light the 2-Wire RS422 or RS485 Communications
selection box. This box will only need to be checked if
the communications with your Modbus Master device
uses a 2-wire RS485 or RS422 interface (see
Figure 5.2). When 2-wire communications are being
used, RTS must be looped back to CTS on the DTU
side of the cable. This can be done on the RS232 side
by looping pins 4 and 5 or on the RS422/485 side by
looping 16 to 18 and 17 to 19. See Appendix D for wir-
ing diagrams for your particular PLC, and whether it
uses a 2-wire connection.
To select the checkbox, click on it with the mouse or,
with the 2-Wire RS422 or RS485 Communications
selection highlighted, press the spacebar. An "X" will
appear inside the brackets when it is selected.
Press the Tab or Right Arrow key to move to the next
field without selecting this checkbox.
Figure 5.2 RS-485 Connector (two-wire)
Communications Settings
Before changing any of these settings, consult your
device manual for the correct settings. To move
between the communications settings, press the Tab
or Enter keys. To select a setting, use the Up or Down
Arrow key to move to the desired setting and press the
spacebar to change your selection.
Siemens Energy & Automation, Inc.
Creating Project Files—Modbus Master to Devices
RTS Control (Request to Send Control)
RTS Control selection is an option provided for
modems or for Modbus Master devices that require
RTS to be active only while the DTU is transmitting to
the PLC.
• If RTS/CTS is selected, the DTU will activate RTS
and wait until CTS is active before transmitting to
the PLC.
• If RTS Delay is selected, the DTU will activate RTS
and wait for the specified delay time to pass
before transmitting to the PLC. When RTS Delay is
selected, the program displays an entry box for
the RTS delay time. Enter the time in milliseconds.
Response Time-Out
The Response Time-Out tells the DTU how long to
wait after transmitting a request to the PLC if no
response has been received from the PLC. After this
amount of time passes with no response being
received, the DTU will assume that no response is
coming and will retry the request. Enter the time in
milliseconds.
Saving Port 1 Configuration Information
Once you have entered all the configuration informa-
tion, select Save to save the configuration to the
project file. Then select Ok or press the Esc key to
close the configuration screen.
If you have changed the configuration and have not
saved it to the project file, you will be prompted to
either save or discard the changes.
Select Revert to return to the last previously saved
configuration without saving any changes.
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