Interface for serial data trasmission between a hearing aid and a control device

In an interface for serial data transmission between a hearing aid and a control device, said interface having a first data terminal for bi-directional data transmission to or from said hearing aid, a second data terminal for a data format sent by said control device having a start bit, and a third data terminal for data to be transmission to the control device, the improvement comprising:

• first coupling means for transmitting data from said second data terminal to said first data terminal;
• second coupling means for transmitting data from said first data terminal to said third data terminal;
• said first and second coupling means being connected to said first data terminal via a common branching point in said interface, said common branching point being settable respectively at first and second logic levels, data being transmitted from said control device via said second data terminal, said first coupling means, said branching point and said first data terminal to said hearing aid when said branching point is at one of said logic levels and data being transmitted from said hearing aid via said first data terminal, said branching point, said second coupling means and said third data terminal to said control device when said branching point is at the other of said logic levels;
• and
• means for augmenting, at said branching point, data sent from said control device to said hearing aid with data inserted into said data format from said hearing aid for undelayed, direct transmission without storage to said control device via said second coupling means.