Modbus Master and Slave Simulators

I needed to learn about Modbus recently, I don’t know it has eluded me for so long living in SCADA-rich Oil and Gas country.

Modbus is a communication protocol for industrial devices developed in 1979 by Modicon, now Schneider Electric. It was originally designed for communicating with programmable logic controllers (PLCs), but has since become popular for industrial sensors and instruments in general. Modbus.org, a U.S. non-profit trade association, now controls the Modbus protocol and provides free access to protocol specifications and technical resources.  

When developing a device which will communicate using Modbus, there may be value in using a master controller or a slave device simulator, or make use of readily-available utility software and libraries.

Master Simulators

A Modbus Master simulator is used to query data from devices and can be a valuable test when developing a Modbus Slave device. A large number of Master simulators are readily available, including free of charge, open source, and commercial software.

Free

QModMaster is a free and open-source Qt-based ModBus master application based on libmodbus (see Libraries below). QModMaster is licensed using the LGPL and includes a bus monitor for examining all traffic on the bus. 

Modbus Tester from Schneider Electric is a free proprietary Windows executable for reading Modbus registers. It supports Modbus RTU and TCP.

Modpoll Modbus Master Simulator from proconX is a free proprietary Windows command-line utility and supports Modbus RTU and TCP. Modpoll is a demonstration utility for proconX’s commercial driver libraries. 

Radzio! Modbus Master Simulator (RMMS).  RMMS is a free proprietary Windows utility (GUI) and claims to replace commercial ModScan and Modbus Poll utilities. It supports Modbus RTU and TCP, and multiple Modbus slave devices. 

Commercial

Simply Modbus Master (RTU and ASCII ). The Free mode allows six request messages before the application must be re-started. C$60. A slave simulator and TCP client are also available. The website has a nice intro to Modbus and Modbus Enron.

Modbus Poll from modbus tools was designed to help developers of Modbus slave devices and others to test and simulate the Modbus protocol. Using a multiple document interface, several Modbus slaves and/or data areas can be monitored at the same time. US$129 per developer. The modbus tools website also has a good intro to Modbus.

ModScan32 from WinTECH Software is a was developed to verify correct protocol operation in new or existing systems. Extensions provide third-party data acquisition using Control Automation routines or the MS Jet Database engine.  A debug mode displays raw serial data to and from a connected device, and ModScan32 can execute test scripts with stimulus messages and expected responses for production testing. Single user license US$64.95. WinTech also provide a number of other Modbus-related utilities. 

Slave Simulators

A Slave simulator provides a source of data for a Modbus Master, and can be useful as a known source of data when setting up a test workflow for a device being developed. A Slave simulator can also be used to create a model of a new device being developed, and act as both the development specification and a source of expected behavior for validating the device being developed.

Free

ModRSsim2 was forked from MOD_RSSIM and seems to be the more active of the two now with a number of updates including compiling on Visual Studio 2010. ModRSsim2 supports RS-232 and TCP/IP connections, the full range of Modbus addresses for all four Modbus types (0xxxxx, 1xxxx, 3xxxx, & 4xxxx addresses), as well as diagnostics with complete traffic byte capture and logging capability. ModRSsim2 supports CSV loading and a scripting environment for testing as well as HTML custom displays. It is free and open-source, and licensed under the GPL.

pyModSlave is a free and open-source Qt-based Python-code ModBus RTU and TCP slave from the developer of QModMaster. A Windows executable is provided and pyModSlave includes a bus monitor for examining all traffic on the bus. pyModSlave is licensed under the LGPL

MOD_RSSIM is a Windows-based Modbus PLC Simulator (and basis of ModRSsim2 above). It is free and open-source, and started as a test program for a SCADA/HMI with Modbus RTU and TCP/IP. Typical uses are to verify device configuration, support development of Modbus master and slave drivers for embedded and desktop platforms, and as an educational tool to learn Modbus protocols. 

Commercial

WinModbus (www.winmodbus.com). Modbus Slave Simulator for Windows. GBP62.50. Lifetime support. 14-day functional demo for evaluation. Polished website.

UnSlave Modbus Slave Simulator . UnSlave simulates any number of Modbus slaves. UnSlave is provided free from Unserver, possibly as a source of test data for Unserver’s Modbus REST API Server, which provides data from Modbus networks and devices to higher-level clients – and is monetized. The Unserver website includes a nice Complete Modbus Guide.

Libraries

A number of Modbus libraries are available.

FreeMODBUS is a free implementation of the Modbus protocol with separate ASCII/RTU and TCP ports for a variety of embedded systems. FreeMODBUS is licensed using the BSD 3-clause license. 

libmodbus is a library for Linux, Mac OS X, FreeBSD, QNX and Win32. The library is written in C, supports RTU (serial) and TCP (Ethernet) communications, and is licensed using the BSD 3-clause license. 

Other Resources

Peter Chipkin has a nice list of various Modbus-related tools.

com0com is a kernel-mode virtual serial port driver for Windows. An unlimited number of virtual COM port pairs can be created, and any pair can be used to connect one COM port based application to another. The module is signed with a test certificate, and requires configuring Windows to load test-signed boot modules.

Microchip PIC24F Development using MLA, EZBL, Git and Dropbox – Part 1

I recently started working with a client on the final stages of a new product development project. The hardware design is based on a Microchip PIC24FJ1024GB610 microcontroller and firmware is being developed on a Microchip Explorer 16/32 development system until prototype hardware is fully tested. I have been working almost exclusively recently with the TI MSP432, and it’s been great fun familiarizing myself with Microchip’s 16-bit development environment. 

Tutorials and demo applications are great sources of information, but are often from the perspective of a single developer, and brush over details such as source traceability and effective team development – often important within an enterprise to reduce risk and expedite time-to-market.

In this new series of blog posts, I will explore using the Microchip Library for Applications (MLA) as the basis of a new project, managing source files in a version control system (Git), sharing a source repository amongst a team using Dropbox, and finally integrating an application with the Microchip Easy Bootloader (EZBL). 

Development Environment Summary

  • Windows 10 development workstation
  • GitExtensions 2.50.02
  • MPLAB v4.05 (necessary at this time to use Easy Bootloader)
  • MLA v2017_03_06
  • Microchip Explorer 16/32 development board with PIC24FJ1024GB610 PIM
  • MikroElektronika microSD click (mikroBUS™ microSD Card module)

Create new MPLABX project

Microchip provides the MLA (Microchip Library for Applications) which includes demo applications which can be used as the basis of a new project. Two important components of the new instrument’s functionality is to present an internal SD Card to a USB host as a Mass Storage Device (MSD), and to support in-field firmware updating.

Based on this functionality, it was appropriate to start with the MLA msd_sd_card_reader demo app, and integrate EZBL after getting the demo code running on the Explorer 16/32 development system, .

Unfortunately the MLA does not include a specific app for the Explorer 16/32 and PIC24FJ1024GB610, so I will have to adapt the Explorer 16 demo app for the PIC24FJ256GB210.

Copy the selected demo app to the ~\MPLABXProjects directory and rename it to something meaningful.

The project directory includes sources files and MPLABX project meta-data.

Now that there are files in the project it’s time to put it under version control. I will use Git for the project source file version control system (VCS), and have installed GitExtensions which integrates with Windows Explorer. MPLABX includes a built-in Git client which can be convenient but is less featured than GitExtensions. I’ll try to show the MPLABX Git client in a future post.

Start by using GitExtensions to create a working Git repo from the project directory.

Create a suitable .gitignore file so that Git will ignore files we don’t need to keep in the repo (generally the intermediate and debug compiler output). MPLABX  project meta-data will be kept in the repo though, as it includes specifying which files the compiler is to use, the include path settings, the target processor, etc. The new project files are then committed to the repo.

The project won’t build yet though because I haven’t copied the MLA support files into the project yet. I’m going to simply copy the MLA framework\ and bsp\ directories into the project. Even though I likely won’ t need all the files, it’s convenient to have a complete and consistent MLA in the project as it will simplify use and maintenance.

The source file directories in the project properties must be configured for the new MLA location within the project directory structure.

The build configuration must also be updated. I created a new configuration by copying the existing build configuration, and renaming it according my target processor and set the new configuration active.  

I also set the target Device to the PIC24FJ1024GB610, and picked the Explorer 16/32 development system in Hardware Tools.

I had hoped the project would build at this point, but at least not complain about missing files. This was not the case. Performing Clean and Build Project produced a torrent of missing files.

Investigating, I first found the build configuration includes specifying the “C include dirs” for the xc16-gcc compiler pre-processor, seemingly duplicating the project Source Directories. I made the preprocessing include directories the same as the Project Properties Source Folders set earlier.

I then noticed that files reported missing in the build output were not shown with a “!” in the project navigator, and they also didn’t have the expected “H” or “C” in their file icon. 

I don’t understand why the files they weren’t found since I had corrected the include file settings. I had thought path settings were all relative to the project directory, but for some reason MPLABX expects the framework directory to be in the root of the drive, instead of the root of the project. Not sure what else to do, I individually removed each include and source file and then used “Add existing item” to re-add each file.

The project still doesn’t build, but now there are no errors due to missing files.

Now that all the files are found, I will commit the updated project to the Git repo.

In upcoming posts, I will fix the undeclared symbol errors, push my local dev repo to a Dropbox repo to share with others, and finally integrate the demo app with the Microchip Easy Bootloader.

For Followup

The correct use of include directory settings is still not clear to me. Manually removing and re-adding each source file would be extremely laborious and error prone in a significant project, and I am concerned I may have made the project non-portable in the process.

There is a note in the Getting Started document for the Microchip Libraries for Applications on this topic, which I need to explore in the future. Point 1 seems to imply though that at least the framework directory must be in the same location on each development system.

Project Include Path Settings

1. Path to the framework folder: In order for the projects to build, the include path up to the framework folder should be
provided for each build configuration and must be placed in the “Includes directories” list in the compiler properties for the
project. The framework module header files expect this. It is already done for the examples provided with MLA, but for the
customer specific project, this needs to be done.

2. Path to system_config.h: For each build configuration, the path to system_config.h needs to be provided.

3. Path to the application project src folder: The hardware independent code resides in the src folder for the application.
The path to the src folder needs to be provided for each build configuration.

For a project to be portable from one machine to another, it is recommended that the paths in the MPLAB X are relative,
while adding files to MPLAB X and while specifying include paths.

(Getting Started, Microchip Libraries for Applications. (c) 2013 Microchip. help_mla_getting_started.pdf, page 11.)

 

 

PLM using Parts&Vendors(TM)

Parts&VendorsTM was the seminal multi-user application in the late 90’s for embedded-electronics design teams to manage parts and assemblies. Running on Windows 98SE (originally), Parts&Vendors managed everything to do with embedded product development, including tracking parts, vendors, manufacturers, purchasing, supporting documents, and even rudimentary stock control for low-volume manufacturing. Teams worked efficiently with more cooperation, less bureaucracy, and at much lower cost, than possible with other solutions of the time.

Parts&Vendors was discontinued in January 2014, almost 15 years after it was released IMHO due to insurmountable technical debt. The Jet-type database did not handle clients crashing or high WAN latencies gracefully, and the codebase had not kept pace with Windows development practices.

Although no longer available, Parts&Vendors remains useful as a gold standard for evaluating PLM capabilities of ERP systems, such as ERPNext and webERP.

Parts&Vendors UX / UI 

Item Master Tab

Parts are accessed through the Item Master tab.

Item Details

Selecting a part provides detailed information on sources (vendors) as well as other useful information.

Files and URLs

Documents and web sites can be associated with a part,

making it easy to access local documents or a web page for reference.

Unfortunately PV did not include a document control user interface to keep things in order, or utilities to verify document paths or list parts referencing a particular file. The shared directory approach worked well for a small conscientious team, or one with a dedicated “librarian”, but not with a more “entrepreneurial” team (if you know what I mean <wink>).

Assemblies

A part may be grouped with others in an Assembly. You can easily tell what assemblies include a particular part in PV from the part’s Used On tab. 

It’s also easy to navigate from a part to a containing assembly, and back. This is also called traversing a product tree containing child parts and parent parts.

An assembly has a Parts List (aka Bill-of-Materials or BOM) that lists its child parts.

Purchasing

Parts can be easily ordered,

An order can accumulate parts until it is placed with a vendor, eventually resulting in a purchase Purchase Order (PO).

In a smaller organization, the engineering team often does the ordering themselves. In a larger organization, a “real” purchase order may need to be created in a separate parallel system (e.g. QuickBooks). The exact process will depend on an organization’s size, structure, and history.

Receiving

When the ordered parts arrive, the PO is retrieved and the order item marked received, 

which updates the stock on hand.

The assembly Parts List is one way to see when the parts necessary to build an assembly are in stock.

Manufacturing

Once all the child parts for an assembly are in stock, a “Kit List” is generated from the “Build” tab for manufacturing. Stock on hand can be reduced for the kitted items, and later increased for the finished assembly when completed. 

Customers

PV can also manage clients and client orders, although the functionality is not integrated with stock control and closing an order does not reduce quantity on hand of the ordered items. The functionality is understandable though given it was never a goal of PV to be a POS (Point Of Sale) or CRM (Customer Relationship Management) system. 

 

This completes a quick refresher of Parts&Vendors. In the next post I will compare ERPNext to Parts&Vendors.