Apparatus for self checking of functional redundancy check (FRC) logic

In an integrated circuit module (200) in which an error detection circuit (236) compares data (204) generated internally on said module (200) with data (108) generated externally from another substantially identical module (100) to thereby assert an error detect output (240) upon the condition that said data (204) generated internally on said module (200) and said data (108) generated externally from said other module (100) do not match, the improvement comprising:

• means (220) for altering said internally generated data (204) by injecting erroneous data into said internally generated data (204) to thereby generate altered data (232);
• said means (220) for altering said internally generated data (204) including first means (224) for digitally storing data, said data being shifted upon application of a clock pulse, said first means being driven by a clock pulse source (201), said second means (231) for combining the output (228) of said first means (224) and said data (204);
• error anticipation means (210) for generating a test condition (216), which test condition corresponds to an expected error condition caused by said altered data (232) at the error detect output (240) of said error detection circuit (236);
• said error anticipation means (210) being a circuit (56) with two stable states that can be changed from one state to the other, said circuit being driven alternately between said one state and said other state by said clock pulse source (201);
• and,
• comparison means (242) for comparing said actual error detect output (240) with said expected error detect output (216).