SW485 – Splitter / extender of RS485

A device for the interconnection of RS485 terminal blocks (bus bars). SW485 enables up to nine RS485 terminal blocks to be connected in a star topology. All the lines are equal. When data are received by any line, they are sent to all the other lines.

What is it good for?

• Enables RS485s to be connected in a star topology.
• Proper interconnection of several devices communicating over RS485.
• Interconnection of RS485 networks.
• Signal edge enhancement for larger distances.

Features of the RS485 splitter

• A device for proper interconnection of up to nine RS485 lines (enables a star topology, which is not usually allowed for RS485).
• Logical processing of all signals.
• Signal transmission with minimum delay – only 130 ns.
• Maximum communication speed of RS485 lines: 1.5 Mbps
• Possibility to configure the switching delay for automatic change of data flow direction (7 µs to 1.9 ms in several increments)
• User-configurable connection of terminating resistors and bias resistors defining the idle state of the line. These resistors may be connected separately for each individual line.
• Mountable to a wall or DIN 35 mm rail.
• Supply voltage 7 to 30 V DC.

How does the RS485 splitter work?

Figure 1: Block diagram of SW485 and connection of several devices (example)

Data from individual lines are only processed by logical circuits. Data received by any of the lines are sent to all the other lines. Individual lines have no buffer for data receipt.

When data arrive almost simultaneously to two lines, the system receives the data whose beginning was first registered. The other lines switch to “Transmission” and start to transmit the data. After the data receipt has been completed the system waits for a configured period of time (a so called “Switching Delay”). After this period has elapsed, all the lines switch to “Receipt” and wait for data to come.