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Here you can find out about Modbus, answers to the frequently asked questions and some troubleshooting tips

What is Modbus?

Modbus is a communication protocol developed by Modicon systems. In simple terms, it is a method used for transmitting information over serial lines between electronic devices. The device requesting the information is called the Modbus Master and the devices supplying information are Modbus Slaves. In a standard Modbus network, there is one Master and up to 247 Slaves, each with a unique Slave Address from 1 to 247. The Master can also write information to the Slaves. The official Modbus specification can be found at

What is it used for?

Modbus is an open protocol, meaning that it’s free for manufacturers to build into their equipment without having to pay royalties. It has become a very common protocol used widely by many manufacturers throughout many industries. Modbus is typically used to transmit signals from instrumentation and control devices back to a main controller or data gathering system.

How does it work?

Modbus is transmitted over serial lines between devices. The simplest setup would be a single serial cable connecting the serial ports on two devices, a Master and a Slave.

Most Frequently Asked Questions…

Trouble Shooting

I can not see any meters when connected

  1. Check to see if the meters you are trying to monitor have power connected to them.
  2. Check the power is connected to the Horizon or management system you have
  3. Check the cables are connected correctly and the terminators are connected to both ends of the LAN.
  4. Check all the meters have a modbus address set.

I can only see some of the meters, not all of them

  1. Check that no modbus addresses are the same they must all be unique
  2. Check that the terminators are at the begging and the end of the LAN, if they are in the middle of the LAN you will see only the meters up to were you have connected the terminator resistor.

Helpful Information

If you are having difficulties in reading all or some of the meters connected to the LAN, start by connecting the first one and prove that you can communicate properly. Then keep adding one meter at a time until you can read all the meters satisfactorily.