GEM80 PLC Systems

GEM80 Controllers

Firstly the development of the GEM80 range of programmable logic controllers began in the late 1970’s. GEM80 became the PLC of choice for major manufacturing industries. Consequently they are found in a diverse range of industries such as Metals, Automotive, Water, Mining, Power Generation, Food, and Oil and Gas.

Popularity of GEM80 PLC’s under the GEC Industrial Controls banner in the Mid 1980’s was extensive. Consequently GEC obtained approximately a quarter of the UK’s PLC market

GEM80 500

Since early GEM 80 controllers operate in the same way as the current models, all allbeit in a few specific areas, GEC/CEGELEC/ALSTOM have a general policy of forward compatibility. Consequently the newer GEM80 controllers will need very few modifications. Allowing older systems to be replaced by the current 400 and 500 series systems

Controller architecture and operation

Lets consider the basic components for all GEM 80 controllers are microprocessor modules, memory modules and a power supply unit. These components are connected onto the central highway, to allow data communication between them.

You will notice central highway consists of a printed circuit board (PCB), containing a number of edge connectors into which the GEM 80 controller modules are fitted. This PCB forms a “backplane” through which memory and processor modules can interchange data.

What components does a GEM80 System contain?

GEM Processors

GEM80 400/500 controllers contain a main microprocessor module. The GEM80 I/O subracks that contain the I/O modules to which the plant sensors and actuator are connect to the processors via the I/O highway ribbon. It is responsible for accepting the input data from the input modules and storing the data in an assigned memory area.

The new output states are calculated after the execution of the ladder program and placed in the memory area assigned to output data. The Processor then moves the output data from memory, transferring it to the output modules in the GEM 80 I/O subrack.

GEM80 Processors also handle serial communication data transfers from the two standard GEM 80 serial ports. You will find each processor transfers data into the serial link assigned memory area as well as transferring data from memory out via the serial ports. As well as controlling the operation of the standard serial links, the serial communication link to the GEM 80 programmer, connected to the programming port.

Ladder diagram execution

Also you will discover the Processor’s task within the GEM 80 controller is to execute the user program. Conseqently you will find the GEM80 Processor requires the state of the input data tables, obtained from the memory having been placed there by the I/O highway. With this information the processor can execute the program.

As a result of program execution the updated states of the outputs are generated. These are then loaded into the memory. Finally the  Processor then retrieves and transfers the data to the output modules.

Memory Modules

GEM400’s can contain memory modules provide a large storage area, that is divided into smaller sections. These are then used for their assigned tasks. Inside the GEM80 controllers memory are different sections of information. This include the following, program instructions, data tables, video memory and mailboxes, used for inter-module message passing.

GEM80 Programmers

System programmer and emulator

All GEM80 systems can be programmed using many different programming devices:

  • Firstly the original GEC Portable programmer circa 1980, a dedicated black box programmer. Required a separate cassette deck and din plug to save and load programs.
  • The GEM80 System Programmer a common site in the mid 1980’s with it’s black front and yellow outer casing. Included a digital tape drive for loading and saving programs. Later models were sprayed in CEGELEC’s grey colour. Enhanced programmers also included a floppy disk drive for program storage, although the formatting is not PC compatible.
  • In 1986 a third party company Advanced Technical Software Ltd produced the System Programmer Emulator the first PC DOS based GEM80 programmer. This more or less copied the system programmer menu screens, apart from the copy compare option. This is due to the fact that the PC had a disk drive rather than the digital tape drive. This product was sold by GEC at Kidsgrove under licence from ATS.


  •  GPP (GEC Projects Programmer) the DOS based programmer was developed in the Mid 1980’s by GEC projects at Rugby. GEC the GPP programmer as their primer programming tool for GEC projects jobs. GPP was not sold as a product, only as part of a GEC project. The format is much the same as the ATS system programmer emulator, the system being a basic system programmer emulator package. 
  • In 1990 the renamed CEGELEC industrial Controls produced a Windows GEM80 programmer called GEMESYS 3 that ran under Windows 3.1 (and now Windows 95,95 etc.). This product had a very slow uptake with most customer’s preferring to stick with the DOS Based ATS programmer which had now been overhauled and named the Universal GEM Programmer.
  • Advanced Technical Software The company updated the basic emulator and developed extra menus, screens and search options to provide the quickest means of programming and monitoring a GEM80 system. Although still DOS based if you currently require a GEM80 programmer this is the option to choose. The latest version is currently version 5.4, use the hyperlink to access their web site and gain full details of this programmer.
  • Advanced Technical Software Ltd’s latest Windows based GEM80 programming package. Is produced in conjunction with Alstom. It can read all formats of previous programmers including GPP, emulator and Gemesys. The AGP is now sold by both Alstom and ATS and is sold as the current programming package for GEM80 systems.

P80 Pilot

  • P80 Pilot is GE’s current day programmer used in all the major industries. P80 Pilot has the advantage over other programmers, because of the fact that a project can contain many GEM80 Controllers as well as drives and RXi controllers.

RXI the replacement for GEM80

Finally GEM80’s have not been manufactured for a number of years, so spares are quite scarce. As a result GE have created a replaced for the GEM80 named the RXi. This modern RXi controller can be used with many different types of I/O. These I/O types include GEM80 I/O, Ethercat and WAGO I/O. 

Also legacy GEM80 program can be take from an old GEM80 PLC and converted with some engineering into a GEM program that can be placed into a RXi. This ladder program in the RXi is edited and viewed with P80 Pilot GE program package.

RXi Controller Replacement for GEM80

See our range of GEM80 courses ...

Want to know more about our full range of GEM80 and RXi courses? Any GEM80 course can be conducted on P80 Pilot, GPP or AGP Advanced GEM Programmer.

GEM80 First Line Maintenance

Essential course for shift craft for faulting finding and monitoring.

GEM80 Maintenance

Maintenance tasks as well as program changes and modifications.

GEM80 Advanced

Next step after the maintanance course includes advanced programming.

GEM80 400/500

Update your knowledge of previous system to the 400/500 systems.


Maintenance tasks as well as program changes and modifications.

RXi / HPCi
E Learning

Maintenance tasks and programming at your finger tips 24/7.