- Option 1: Modbus connected to the FC Bus terminals.
- Option 2: Modbus connected to USB through the USB-to-RS-485 adapter, if the FC Bus is unavailable. The SNx engines include built-in RS-485 ports which are primarily intended for legacy N2 or BACnet MS/TP protocols. If these protocols are in use and you do not have an RS-485 port available for other third-party integration devices, use a USB-to-RS-485 adapter to connect third-party integration devices.
- Option 3: Modbus connected to USB through the USB-to-RS-232 adapter. Use this option if a single third-party device is connected and requires RS-232 connection.
-
Choose the applicable option from the following table and complete the
associated procedure.
Option Procedure Option 1 For a Modbus RTU protocol that requires an RS-485 serial connection, connect the 2-wire bus cable to the removable 4-terminal plug labeled FC BUS-1, as shown in Figure 1. If you have the SNE2200x model, you can otherwise use the second terminal plug that is identical in function and labeled FC BUS-2. The RS-485 bus is a two-wire network.
Note: When the FC BUS-1 connection is used for Modbus integration, it is not available for BACnet Field Controllers or the CWCVT.Option 2 Connect the USB adapter, ACC-USBRS485-0, to the USB-1 or USB-2 port and connect the RS-485 based third-party integration to the USB adapter. Option 3 For a Modbus RTU that requires a RS-232 connection, use the USB-to-RS232 adapter, code number ACC-USBRS232-0. Connect the adapter to the USB-1 or USB-2 port and connect the three wires to the Sub D9 interface on the USB-to-RS-232 adapter as follows: Rx to pin 2, Tx to pin 3, and GND to pin 5.
Note: The maximum cable length between devices connected though an RS-232 line depends on the baud rate used. For example, if the device communicates at 9600 baud, do not exceed a cable length of 49.21 ft (15 m).Figure 1. FC Bus terminal connection for Modbus devices (Modbus connection Option 1 and Option 3 shown)Callout Description 1 USB connection: Connect USB cable from SNE to RS-232 converter
2 USB-to-RS-232 adapter
3 To Modbus devices 4 FC Bus terminal connection -
When you use a RS-485 connection, you can add additional vendor devices. To add
additional vendor devices, wire from one device to the next as shown in the
following figure. Do not connect more than two wires to each terminal to ensure
that a daisy chain configuration is used. For general Modbus protocol rules, see
Wiring considerations and guidelines. For a RS-232 connection, you can connect
only one vendor device.
Figure 2. Modbus RTU wiring detail: daisy chained devices