5 Creating Project Files—Modbus Master to Devices
5.5Modbus/Passthrough Setup—Port 3
Port 3 can be used for passthrough communications to your Siemens SEAbus devices or for connection to a second Modbus Master device. Passthrough com- munications enables a PC running WinPM, or other supervisory software connected to port 3 of the DTU3005 to communicate directly with the SEAbus devices connected to port 2. In passthrough mode,
any messages received on port 3 of the DTU are sim- ply “passed through” to the devices.
Passthrough communications are not available for VDEW devices; see Section 5.3 for Port 3 (Modbus Master) configuration of VDEW devices.
You must have a Modbus Master to Devices project file open to configure port 3 using the instructions in this section. Select Port 3 (Modbus/Passthrough) from the Edit menu, and the Port 3 configuration screen appears.
The first option on the configuration screen allows you to choose connection to a second Modbus Master device or passthrough to port 2. Select the appropriate configuration with the mouse, or use the Up or Down Arrow keys to highlight the selection and press the spacebar.
Modbus Master
If you select Modbus Master, the screen appears as shown above. Select the Modbus protocol by select- ing the Modbus Protocol list box, highlighting either ASCII or RTU, and pressing Enter. After you have selected your protocol, press the Tab key to highlight the Modbus ID selection box. The Modbus ID is used to identify which Modbus Master device the DTU is to communicate with. Type in the Modbus ID number and press Enter.
The remaining configuration selections are for the communications parameters and have the same choices as those for port 1. Refer to Section 5.3 for instructions on these fields.
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