Abstract: In order to expand the address range of the program counter in a microprocessor, a register is provided as an additional special-function register which actually consists of two separate registers which are connected in series. One register supplies the most-significant address bits via an AND-gate and is also coupled to the internal data bus. The register contents are automatically changed when the program counter passes the end position or the starting position. In the case of program jumps, the old contents of the register are also stored in the stack; this requires only few additional instructions from the standard instruction set. In the case of an interrupt, the AND-gate is blocked, so that automatically the first segment of the program memory with the interrupt programs is addressed. A linear expansion of the program address range is thus achieved without degrading the compatibility.