Digital trigger for oscilloscopes

The circuit described here enables an oscilloscope to be triggered when a predetermined binary code word is applied to one of the circuit's inputs. lntegrated circuits ICI and IC2compare the 16 input levels with the code set by switches 51and 52.If one of the inputs has a dataword that is equal for not less than 100 ns to that set by 51and 52,pin 19 of ICI goes high. Note that, because of the pullup resistors, open inputs are treated as high.