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Connecting to UniPi extension

The UniPi extensions are convenient way how to extend the number of inputs and outputs at one location, or make accessible at another one.

The communication between controller and extension is via RS485 ports. The extension acts as a Modbus slave, which has an extended support in the Mervis.

You need only two cables to connect the UniPi extension to the controller. Just interconnect the RS485-A port on the controller to RS485-A port on the extension and RS485-B on the controller to RS485-B on the extension.

For communication to work, you have to have identical serial port parameters on both sides - speed, data bits, stop bits and parity. Also each extension unit has to have unique Modbus address. You can set those in two ways: by HW DIP switches, or in the Mervis.

DIP switches

The DIP switches are small levers, which can be pushed down, or pulled up. When the lever is pushed down, the function is enabled.

On model xS10, xS30 and xS40, you can set the speed, parity and address by DIP switches. On the xS50, only the DIP switches for address are present on the unit.

The first DIP switch is called RS485-END. It is for connecting and disconnecting 120ohm resistor between RS485-A and RS485-B for proper termination of the RS485 bus. You will have to enable this option when the extension is last device on the bus. Typically, this applies to very long buses, over several 100s of meters.

Second DIP switch is omitted, without any function.

The third to sixth DIP switch is for setting address. With these switches, you can set address from 0 - 15 in binary format.

Address DIP sw. 3 DIP sw. 4 DIP sw. 5 DIP sw. 6
0 OFF OFF OFF OFF
1 ON OFF OFF OFF
2 OFF ON OFF OFF
3 ON ON OFF OFF
4 OFF OFF ON OFF
5 ON OFF ON OFF
6 OFF ON ON OFF
7 ON ON ON OFF
8 OFF OFF OFF ON
9 ON OFF OFF ON
10 OFF ON OFF ON
11 ON ON OFF ON
12 OFF OFF ON ON
13 ON OFF ON ON
14 OFF ON ON ON
15 ON ON ON ON

The seventh switch is for setting speed of the serial bus between 19200bps (OFF state) or 9600bps (ON state).

The eighth switch is for setting parity of the serial bus between Even (OFF state) or None (ON state).

The xS50 has DIP switches only for the address. Other parameters of the serial port has to be configured in the software. The default settings are as follows: 19200, 8 data bits, 1 stop bit and no parity.

Software settings

The connection parameters can be also set in Mervis. The HW settings takes precedence, so in order to SW settings take place you have to set the address to 0. The rest will be described later in this tutorial.