To someone skilled with this, they can use the “logic” page in the DDC software to troubleshoot problems. When this program is downloaded into the controller one can use the logic page in the DDC software to observe real-time information from inputs to outputs to alarms and schedules. Everything from And gates to Or gates to Timers blocks to complex mathematical blocks allow a DDC Control programmer or DDC Control engineer to assemble programs in little time simple by arranging a set of logic blocks in a software program and then compiling this set of logic blocks into a basic machine line code and necessary tables which the casual observer and even the engineers never see. These are the basic logic blocks that, when combined, make up the DDC algorithm control program. Some of these logic blocks are rather complex but others are very simple. Some software and hardware manufacturers utilize symbols to build their logic programs for HVAC DDC control. DDC Programming Logic Symbols 1 - DDC programming in HVAC Control can be rather complex especially to those who don’t understand software or programming.