This attribute indicates which specification the IISP interface
complies with. The options are iisp10Sig30 which refers to IISP
version 1.0 with 3.0 signalling and iisp10Sig31 which refers to IISP
version 1.0 with 3.1 signalling. If this attribute is changed, all
switched Vcc components in this interface are cleared due to the
fact that the two versions are incompatible.