The document specifies the electrical and mechanical requirements for an interface device to allow a general-purpose control device such as a desktop computer to be connected to hearing aids, for the purpose of electrical setting of their parameters. It is restricted to the digital interface between the control device and the hearing aid. The specifications are for use in connection with hearing aids with parameters set by a direct electrical connection using a cable. They do not cover hearing aids with parameters controlled by radio frequency or infrared transmission, or any other wireless method of control.