Frequently Asked Questions
Q. How do you share development costs for ports?
A. When customers ask for a port that we do not have, we offer a fixed price that includes hardware and the software
engineering effort. We share the cost of hardware and the engineering effort. In this way the customer gets a
developed and tested port for a very attractive price.
Q. Does your MODBUS solution support both RS485 and TCP?
A.. Yes. At present our code is compile time configurable to support Modbus RTU (RS232/RS485) or Modbus TCP.
Q. What is your licensing and pricing model?
A.We have two licensing models, Multiple Product and Single Product.
The Multiple Product license is designed for manufacturers of end-use equipment, sensors, meters, and other data acquisition hardware. They can use the Modbus library for unlimited number of end-use units for all their products. The price for one Multiple Product License library is USD 1,000.00.
The Single Product License supports design engineers, product developers, consultants and integrators who require Modbus for a single product that they are working on. The library can be deployed on multiple end-use units of the design. The price for one Single Product License library is USD 500.00.
Q. How is the documentation for the source code delivered.
A. Documentation for the source code library is available on our website.
Q. Why most of the modbus serial to ip devices only work when the ip device is the master and the serial device is the slave?
A. Generally Modbus IP devices are Human Machine Interface(HMI's) that needs to communicate with many serial remote terminals (barcode readers, temperature controllers, pressure sensors etc.)
to acquire data from them or send control signals. Now since HMI is one for a control system with many RTU's, it invariably becomes the Modbus Master with all terminals acting like slaves.
Q.I have a Pololu servo controller chip which needs to be hooked up to a Galil RIO PLC. I have read that once this is done,
my data to the controller will be sent via ModBus. Could someone give me some idea as to what kind of function code
I'm going to need to send a signal to the servos? This is what the Pololu website says the controller needs to receive:
A. The spec that you reproduced from Pololu website only talks of the physical layer (baud rate, parity, signal
levels etc.) and not of the Modbus register map. Usually in PLC's where you create tags (variables), there is a provision
to assign Modbus register addresses to them. Sometimes, the PLC software may auto-assign the addresses as you create
tags/variables. Please check out the Users Manual of the PLC software and you will find some answers.
Non-programmable devices (e.g. a pressure meter capable of Modbus communication)
have fixed register maps and the OEM usually provides a table of this map in the device's Users Manual.
Q. I have bought both Modbus Master and Slave libraries from Colway Solutions and my board can be a master
or slave depending on user selection. The integration of the two stacks generates some conflict. How can I resolve this?
A.Since you are using our both libraries on the same CPU, the contention is because of macros with the same name present in master
library and slave library. To resolve this, please rename all of such macros with a different name.
Q. There are temperature controllers (25 nos.) at different locations in one big room sensing temperatures using PT-500.
The temperature data and other status details like Oven On/Off, etc. to be transmitted and collected at one dedicated pc. A report using this data to be made.
We are using RS-485 interface.Can we use Modbus for this application? How to do it? Can it be a cost effective solution?
What are the steps involved? Do we require any additional Hardware/Software?
A.Can we use Modbus for this application?
>>> If the temperature controller that you are using is Modbus compliant then you can certainly use
Modbus for this application. This would entail writing an application on the Host PC that acts as a
Modbus Master and then communicating with the temperature controllers. If the controllers are not Modbus
compliant, then you cannot use Modbus here unless ofcourse you are the designer of the temperature controller
and so have the option of adding this support to it.
How to do it? Can it be a cost effective solution? What are the steps involved? Do we require any additional Hardware/Software?
>>> If the controllers are already Modbus compliant, then all you need is a Modbus Master library for the host.
You can then write your application in VC++ or VB or C# using this library and do all the application
logic you want to. Alternatively, there are SCADA applications that already support Modbus and you could
use them if you do not want to write software at the C/C++/C# level. If you are the designer of the controllers
and would like to add Modbus functionality to it, then you need a slave library for the micro controller used in
The only additional hardware that I think you will need is an RS485 card for your host PC. You can also use a
USB to RS485 converter for this purpose.
Q. We have a PLC (Festo CPX) and robot, and we are trying to establish Modbus TCP between the two.
Looking at the documentations for these, it appears that both of them can only function as slaves (servers).
Is it possible to establish a server to server communication in this case?
A. No, It is not possible to have a server to sever communication, instead it is a client to
server communication where client send a request and server respond back. You can have one master
which communicates with both PLC and robot.