The stalled dot matrix printer
"The serial link was a little temperamental (particularly if the printer had gone offline for any reason and the buffer was full), but it usually "just worked"."
That reminds me of the dot matrix printer which spewed out packing lists for the warehouse.
It mysteriously stopped one day and no amount of coaxing would bring it back to life. I could see from the console in the computer room that the program was trying to perform output. Killed that process, restarted it, no joy.
In the end I plugged the printer serial line into a nearby VT52 and pressed CTRL/Q. Hey presto, the picking lists started "printing" to the VT52.
Line noise must have generated a CTRL/S down the line to the CPU.
It only happened two or three times in the next three years.