This is a sixteen-bit wide register which can be loaded with data from the data bus (using ICNR) to indicate the classes to which the device belongs. Only the lower ADI chip register is required for this function. The register in the top ADI will be loaded from the data bus, but when CSR#7 is read through the multiplexer, the upper 16 bits are replaced with zeroes. (See also Section 7.2.10.) This register may be used for other purposes such as CSR#04 (Device User Address Register) or CSR#01 (User Defined). This is made possible by providing another multiplexer code which reads all 32 bits of the register.