Testing of storage part of control unit in telephone exchange - monitoring number of program pseudo commands inserted into series of program commands with false parity bits

摘要

The telephone exchange control unit has a processing part and at least one storage part in which programme commands are stored, security by parity bits. During a pause in the storage part (S) operation all storage locations (W1...Wn) are consecutively interrogated for the parity bits testing, during which carrying out of programme commands is blocked. The number of programme pseudo commands inserted into the series of programme commands and provided with false parity bits (F) is monitored. In operation they are skipped by skipping commands. An error alarm is delivered if, during testing, an incorrect number of programme commands with false parity bits is found.