Title: The Wall

Dear Francis,

Further to my two articles about bit pattern techniques, those collecting them may be interested to know that you can use bit patterns for simulating faulty digital circuits. In the simulation of normal circuits, each wire can be 0 or 1, and the simulation of a gate might involve doing a logical AND, OR or NOT operation. If, instead, this operation is done in parallel on all the bits in a word, then a number of circuits can be simulated in parallel, and different faults can be introduced into each one. This has applications in discovering if a particular fault will show up in a test suite.

Also, the one-byte bit reversal function was wrong. Since only the bottom 8 bits of the return value are significant, it needs to be AND-ed with 0xFF. This was implied in the text but not explicitly stated.

Silas S. Brown