Providing a master device with slave device capability information

In a system having a master device coupled to a slave device by means of an interface, wherein a function of the master device includes downloading a control program to the slave device, an apparatus for providing the master device with capability information corresponding to the slave device has hardware for reading the capability information from a predefined portion of the control program, and hardware for storing the capability information for use by the master device during a communications operation with the slave device. An encoding scheme for the capability information permits new functions to be added without having to re-encode pre-existing information corresponding to pre-existing slave devices. The capability information is encoded as a first vector and a second vector. A new function that is supported by a new slave device is added to the first vector when the new function is not supported by any pre-existing slave device. Default values are provided for pre-existing first vectors, to indicate that the new function is not supported by the pre-existing slave devices. Similarly, a new function that is supported by all pre-existing slave devices but not supported by a new slave device is added to the second vector, with appropriate default values provided for pre-existing second vectors.