ASIC/2 HVAC PLC serial bus interface experiments.

The purpose of this project is to document my exploration of the communications bus used to exchange information between ASI Controls HVAC control equipment - particularly my analysis of the structure of the data packets used to transfer information between the devices.

Using the acquired knowledge of the packet structure, I have been able to construct and code an Arduino based device that can successfully send and receive data on the bus.

Using my knowledge of the internal data structures of the ASIC controllers, I can obtain and display temperature values and other data using this device.

System Description

The HVAC system being investigated is for a factory administration building. It is fairly basic and consists of 3 control components:

  • ASIC/2-7040 “Configurable System Controller”
  • ASIC/2-8540 “Configurable Unitary Controller”
  • UnioOP - ePAD04 Human Machine Interface (HMI) panel.

The “ASIC/2” controllers are for I/O control and are made by ASI Controls.

ASIC produce programmable control equipment primarily for Heating, Ventilation and Air Conditioning (HVAC) applications.

The “UnioOP – ePAD04” HMI panel provides an operator control interface and is made by Exor.

These three hardware devices are linked by an RS-485 serial communication bus.

Above: ASIC/2-7040, ASIC/2-8540 and ePAD04 as installed.

Programming and configuration of the ASIC/2 controllers and ePAD HMI is performed using proprietary software packages.

For the ASIC/2 controllers, this package is “Visual Expert”

For the Exor HMI panel, this package is “Designer 6”.

I have access to a licenced copy of each of these software packages. I will NOT provide free copies of these software packages. Please do not ask!

Background and rationale

I am responsible for electrical and control system maintenance at the factory where this HVAC system is installed.

This project started with the idea of creating a display to show a temperature profile of the office over time by plotting the room temperature sensor data.While this is possible using the “Visual Expert” programming software, the function is intended primarily for commissioning and fault finding and is not a practical long term solution.

The common method would be to purchase, install and configure an additional HMI display panel or purchase a licence for specialised software from ASIC that allows a PC to be configured as such a display, however both these options are relatively expensive and I knew that I would certainly not get purchasing approval for such software or equipment for this trivial application.

My primary job function is understanding and maintaining the control systems of our industrial production equipment.I also enjoy making my own hardware (for non critical applications) and have some experience with micro controllers (particularly the Arduino platform) as well as general programming experience and electronics knowledge.I therefore decided to see if I could build my own interface.

My usual first step is to consult whatever technical documentation is available.

ASI Controls technical support model depends on the use of “Value Added Resellers” (VAR’s). For ANY and ALL enquiries regarding technical details of their equipment and software (beyond the most basic data sheets), ASI Controls inevitably refers to you to your local VAR.

I happen to live in a city of about two million people, of which exactly one is a ASI Controls VAR.This person has a business to run and (not surprisingly) is somewhat disinterested in providing free technical support.

ASI Controls has ALL technical documents and manuals locked away behind firewalls only accessible by VAR’s. This applies even if you have legitimately purchased...

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