Circuit preventing evaluation of simultaneous operation of keys - scans keyboard and has control circuit permitting or blocking key operation evaluation

摘要

The keys belong to a digits and/or function keyboard of an operator's position in a telephone PBX. The keys are arranged in a matrix in rows and columns by a timing control. When each key operation is detected, a signal is applied to a control device which delivers at the end of each complete matrix scanning a key evaluation permission or block signal, depending on the number of detected key operations. These signals are evaluated only once for each key operation using an intermediate store.