An interface system for communicating between a programmable device, such as a hearing assisting device, and a programmer unit employs a circular shift register and a memory. Upon initialization the memory contents are loaded in the circular shift register and cycled through so that each bit is exposed to the programmer unit for verification or change. After a complete cycle through the shift register the program is fed back to the memory where it is used to control the transfer function of the hearing assisting device. By use of this circular shift register only two connections to the programmer unit are required, thereby minimizing the mechanical size of the connector needed to connect the programmer unit to the hearing assisting device, which may be an in the ear device. A low voltage version of the interface system uses current sources and a high voltage version of the interface system, such as used for a remote controller, uses impedances and a voltage source.