GPS positioning is a well-known positioning system and used in several applications. However, these signals are sent with low power and do not penetrate walls and have problems in urban areas with tall buildings. On the other hand, GPS shows advantages compared to other technologies when used outside. Since timing is one of the most important issues when it comes to positioning, some of the timing tools from the GPS can be helpful in other positioning systems. Using terrestrial communication such as television signal, which is designed to penetrate into people’s houses, makes it possible to positioning indoor and in urban areas as well. Still, this is not designed for positioning use, and there are more possible positioning errors. Depending on what the positioning is used for, the accuracy with TV signals may be enough, but when used in violence alarms and for firefighters there is a need for much higher accuracy. It is also important that the altitude can be decided. The Pseudo Television Transmitters (PTT) system has been designed for high accuracy positioning indoor, where it is crucial to reduce errors. Especially the timing and start up order is important and one of the technical things we can control. The rest of the error is often caused by multipath, and bad geometry on the transmitters. The PPT system consist of GPS receivers who give the absolute position for the transmitter, baseband transmitters with special designed antennas which broadcast the TV signals, Software signal generator, filters, and amplifiers. There is an interface controller which connects and controls all the parts and which the communications goes through. In the system discussed and the applications developed in this paper, GPS has been used as a helpful part of the system. The system needs to use GPS for absolute positioning of the baseband receivers, and provides an in common clock for the total system. It also provides a 1 Pulse per Second (1PPS) signal which is used as a reference to make the system work together in the best way. This paper has focused on the interface controller which is the communication between the parts in the system. One of the most important parts is to optimize the timing and have a start-up sequence where the accuracy errors are reduced as much as possible. This paper is written at and for Rosum Corp, and development done is used in a system which will run live, already sold to a customer. To be able to make an optimized interface controller, a hardware unit is chosen regarding to the specification, and the start-up sequence developed, implemented and written in the programming language C.