Project Description

TelePro designed and implemented a communications system between an IBM PC platform, used as a Human-Machine Interface, and a wide variety of Process Control Host systems. This communications system would be responsible for transferring data between the Microsoft DOS based display system and a variety of host processors.

Communications media supported would include:

  • serial asynch
  • frame-level Ethernet
  • TCP/IP
  • Manufacturing Automation Protocol (MAP)
  • Host processor & operating systems included:
  • HP/UX
  • Modcomp / Max IV and Max 32
  • Modcomp (Motorola) / RealX
  • Modcomp (PC) / PC-RealX
  • DEC Alpha / DecUnix

The communications interface would provide access to variables defined in multiple global common areas, binary file-based variables, high speed process variable trending, and historical data trending.  It also reduced the CPU resources required on the process control systems.

System Solution

HMIC Architecture

A communications protocol was designed to implement data transfer between multiple hosts and the HMI product. This protocol, and the programs that support it, were implemented on the HMI product and then each of the required host systems.

This implementation had the following features:

The protocol was designed in layers to allow easy implementation over many media.

All data transfer was done in binary in the local format of the host processor to minimize host system resource utilization.

The coding was done in C to minimize the work involved in re-hosting the software.

A data dictionary was implemented to provide for English readable names for data variables used when building screens for the HMI system. The screen designer used these names to describe the variables associated with textual data areas and graphical components.

The host process resolved these names into the proper variable locations when the operator initially requested a screen. All following dynamic data requests used this address for low overhead access.


The system was first demonstrated on a rolling mill application using an asynchronous serial interface. The process system saw in increase of 11% in available CPU resources when the old operator display system was replaced. Follow on implementations included screen swapping and graphical variable display updates which exceeded requirements (200ms to display a new screen with data, 70ms screen update rates).

Installations using the underlying TCP/IP protocol and Wan media allowed viewing and modification of data on process control systems at remote locations from engineering support centers.

The HMI system has been implemented on additional new and retrofit applications resulting in cost savings by transferring standard applications and features.  The system is installed corporate wide at multiple plants in the US, Europe, and Australia.