Multiple instructions can be microcoded into a single instruction time by setting multiple of these bits. The bits are assigned meaning in groups. We begin with group one. The last few bits of OPR's group one encoding are most easily decoded with another dispatch. The simulator reads commands from a file.
Most commands correspond to front-panel switches or buttons.
A few more control the loading or punching of tape at the teletype. The remainder measure and report progress within the simulation job. This program has been formatted to be read by a wider audience than originally intended. A careful programmer also watches for functional unit conflicts and in-stack loops. The coding conventions were adapted from Greg Mansfield, author of the MACE operating system and many of the tools and utilities that ran on it.