Abstract: For assisting the self-test of circuits with unequiplebable random patterns, a logic module is provided which is composed of two types of basic cells. Each basic cell contains a register cell and a sub-circuit composed of gates. Dependent on two control signals, the basic cells can be operated as a normal register, as a shift register or as a linear feedback shift register. In the operational mode as a linear feedback shift register, the logic module can be used as a random pattern generator. To this end, the logic module is divided into a first module and into a second module. The first module contains an interconnection of two types of basic cells and a combinational logic system which operates the one part of the output signals of the basic cell in accordance with a Boolean function. The operational result is supplied to a second module of identical basic cells which operates as a shift register.