With the replacement of part of the old 3.5m electronics  by VME computers, a concept was developed to adapt the dome guiding system and to use Programmable Controlers (PC).
The dome hardware changes and the programming of the PC's were carried out by the Calar Alto team.

• The most important difference with the old dome guider is that the VME-TECS system links with the dome through a single serial interface. A command list was created and the VME-TECS programs adapted. In that way the old complex parallel interface could be changed and 90 VME inputs and 20 VME outputs could be saved.
• The old contact rails serial interface used to communicate with the moving parts of the dome were eliminated. This change removes  a frequent source of error in the past. The old interface worked with a specific Zeiss protocol which was very difficult to adapt to VME concept. It was replaced by a wireless communication, by means of radio modems and a completely new communication protocol. The data exchange is now done through the PC programs only.


Most of the dome functions are executed from a movable control console (Engineering Console). The console is separated from the TECS-VME, and the communication is provided via a wireless link which is independent from the VME system. The use of a thick trailing cable as done in the former setup is thus not required any longer. The Engineering Console is no longer linked to the TECS bus system and communicates with the Dome/VME directly.

Through the use of the PCs, a lot of new possibilities are available now as a certain intelligence has been assigned to the dome.  All functions except for those dealing the telescope maintenance platform are driven by means of the PC program. The "dome automatic tracking" program which has been part of the old TECS  has been taken over by the PC.
The new VME system provides the telescope elevation and azimut values only, through a serial interface.

The automatic telescope top ring change is now performed from the dome control. The dome PC sends, through the serial interface to the VME system,the commands to execute a change. The automatic front ring change is not yet fully tested and will be implemented later.

The control of the various dome functions is managed by three decentralized PCs.
The PCs communicate with each other through a wireless link. Each PC sends, continuously in one string, the respective complete system status.

Which one of the various PC programs is active depends on the kind of service type that has been selected. The possible service types are:

• Only dome service (without TECS and Eng.Desk), PC1 and PC2.
• Astronomical service (dome tracking with TECS), PC1 and PC2.
• Engineer service with TECS (manual system change), PC1, PC2 and PC3.
• Engineer service without TECS (crane, dome rotation, gates), PC1, PC2 and PC3.
• Automatic system change with TECS, PC1 and PC2.

A major concern arose about the use of wireless communication. During the initial phase of the project, various tests were carried out.
A first type of radio modems could not be used because of disturbances which were caused by reflections at the dome walls. They had to be replaced by special radio modems with operate at the low transmission power of 15 mW only. A redundant communication system was devised. If the PCs encounter an interference, they switch over to a second radio link in a different frequency band. The sequence is known as "Frequency-Hopping".