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Modbus FAQ

Frequently Asked Questions (FAQ)

Modbus TCP

What type of protocol is Modbus TCP?

  • Modbus TCP is an open protocol and is widely uses across building automation, intelligent buildings, and industrial automation networks…Read more

What functions can be performed by Modbus TCP to retrieve information from a device?

  • With the help of a FieldServer client we can set and retrieve Modbus TCP values from your device and make it available to just about any other devices…Read more

Tell me more about Modbus TCP data conversion

  • Modbus TCP supports various Modbus functions and data types and scaling/bit packing can also be applied…Read more

What is the minimum subset of function that a Modbus salve device should implement?

  • It depend on if you are creating a commercially available slave device or your own slave device. If you are creating a Modbus Slave device that will only be interrogate by a specific Modbus Master, then you only …Read more

We want to check the communication between our device and personal computer, so we need the 232 communication software?

  • There are a few free utilities to check communications between your PC and your Modbus device. Try searching Google for Free Modbus Slave utilities…Read more

Modbus to Modbus – A Simple Way to Convert Serial (RTU) to TCP/IP and TCP/IP to Serial (RTU)

  • In an assembly where the Fieldserver device is reading from a Modbus device on Modbus RTU (Serial) or Modbus TCP/IP (Ethernet), and then serving to another Modbus device on Modbus TCP/IP or Modbus RTU, i.e., if the Fieldserver is integrating from Modbus to Modbus – RTU to TCP/IP or TCP/IP to RTU, then…Read more

Modbus/TCP to BACnet/IP Configuration Sample

  • This example FieldServer configuration illustrates a config which reads data from a Modbus/TCP device and makes the data available as BACnet data. A remote BACnet client can read and write points. Relationship between a connection, node and Map Descriptor for a client The name of the connection/adapter…Read more

Utilizing Modbus Scanner to Write Registers of Digitrip 3000 (Protective Relays) Controls

  • Introduction Digitrip 3000 Protective Relays are manufactured by Cutler-Hammer (Eaton Corporation). Typically, Modbus TCP registers are provided as control registers for these Digitrip 3000 Protective Relays in the Digitrip 3000 Control documentation. It is very important to note that ALL of these…Read more   

Modbus RTU

How are real (floating point) and 32-bit data encoded in Modbus RTU messages?

  • The Modbus RTU protocol itself was designed based on devices with a 16-bit register length. Consequently, special considerations were required when implementing 32-bit data elements. This implementation settled on using two consecutive 16-bit registers to represent 32 bits of data or essentially 4 bytes of data. It is within these 4 bytes of data that single-precision floating point data can be encoded into a Modbus RTU message…Read More

Why are 7 data bits bad for Modbus RTU?

  • Modbus RTU is a binary protocol. It requires the use of all 8 bits in each character / byte that forms the message because there are many situations where the 8th bit is used…Read More

Can I create a Modbus Client using C#?

  • You should be able to write a Modbus client in any language that has access to the serial ports or a TCP connection. C# has access to both the serial port and a RAW TCP connection, therefore it should not be too hard to create a simple Modbus Client with C#…Read More

What is the minimum subset of functions that a Modbus slave device should implement?

  • If you are creating a Modbus Slave device that will only be interrogated by a specific Modbus Master, then you only have to implement the functions that the Modbus Master will use to call on your Modbus Slave.
  • If you are creating a commercially available Modbus Slave device there are 4 so called classes of function implementation…Read More

What is a ModHopper wireless transceiver?

  • The ModHopper wireless transceiver is a premier, low-cost product for building automation applications developed by the Obvius Corporation that supports Modbus and pulse equipment (i.e. sensors, meters, etc.) along with related networks. The ModHopper transceiver is best suited for energy monitoring in either industrial or commercial structures…Read More

Where can I find more Modbus developer resources?

  • The internet offers a wide variety of sites related to Modbus development from personal to commercial sites. One major resource site is the main Modbus website. Another great resource is our own Modbus Protocol Specification. Read more for a breakdown of the tools offered on the official Modbus website…Read More

How can I convert 16-bit numbers to 32-bit numbers in Modbus?

  • FieldServer provides 4 functions to convert Modbus 16 bit numbers to 32 bit numbers. These functions take two 16 bits numbers to form one 32 bit number, and each function processes the bytes in a different order…Read More

How can I connect multiple clients to a Modbus slave?

  • The solution is to use a multi-port FieldServer. Connect each client to its own port and the slave(s) to thier own ports. Each client will see a single virtual slave(s) on its network. This not only solves the problem but is extremely efficient. Of course the FieldServer needs to be correctly configured…Read More

How do I test for a connection between my Modbus device and my personal computer?

  • There are a few free utilities to check communications between your PC and your Modbus device. A quick search on Google for “Free Modbus Slave utilities” should give you a list of utilities to chose from. You can also try using our own CAS Modbus Scanner. It’s free and very easy to use…Read More

Gateway Selector

Select your combination of protocols.
Protocol 1
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