Method for identifying errors in data processing systems, in particular telephone switching systems

In a telephone switching system, a plurality of peripheral control sub-units (1P, 2P, nP) and at least one central device (Z) are provided. A code word from a preceding test polling is stored in a control sub-unit under test and is supplied as a test acknowledgement in a subsequent test polling via a line system shared by a plurality of control sub-units to the central device. A new code word is simultaneously supplied to the respective polled control sub-unit. In the central device, the transmitted code word is compared with the recorded code word. If the comparison indicates an error, error location is initiated.