Siemens DTU3005-B manual RS-485 Connector two-wire

5 Creating Project Files—Modbus Master to Devices

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.

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.

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.

Response Time-Out

The Response Time-Outtells 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.

Siemens Energy & Automation, Inc. 31