To get a HIGH(1) output from an OR gate, one or more of the inputs must be HIGH(1). If all inputs are LOW(0), the output will be LOW(0). Looking at the truth table, all except TRUTH[0] fulfill this requirement. This means that TRUTH[1] to TRUTH[7] must be HIGH(1) and TRUTH[0] must be LOW(0), giving the hex value 0xFE to put into the TRUTHn register.
Figure 1. OR Gate
