A good way to start a display hack. It will run both on ITS and out of timesharing equally well.
this post was submitted on 16 Aug 2023
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Explanation. The program starts at GO and attempts to use the .IOTLSR system call to enable the job to use I/O instructions. Running under ITS, this succeeds and goes on to the CONO instruction which resets the display.
Out of timesharing, there is no operating system UUO handler for the .IOTLSR call, so the program will jump to the UUO handler at location 41 which just jumps back to the main program.