1. Error detection apparatus for verifying the correctness of a binary coded constant, said apparatus comprising: code conversion means having a plurality of input terminals for receiving signals representative of said binary coded constant and a predetermined number of output terminals, said code conversion means being operative in response to said binary coded signals to produce output signals coded in a predetermined manner; selection means coupled to only certain ones of said predetermined number of said output terminals; and, check circuit means including a predetermined number of input terminals coupled to said selection means for receiving coded signals from said only certain ones of said predetermined number of output terminals, said check circuit means being operative to generate a check signal in response to said coded signals applied to said input terminals for signaling that said constant is valid and the error free operation of said code conversion means.