Cabling up the insides of my uPDP-11/53 would have been easier if I had found this:
…which was taken from page 20 here. So I’m keeping a copy, for possible future reference.
My RT-11 boot disk with DECUS C worked a treat on the real machine. It took 16 seconds for it to draw the mandelbrot set in ASCII art on the actual uPDP-11/53. Here is a picture of the real thing in action:
I would say that's a result. My next project is to use memory-mapped I/O in C to communicate over the second serial line. This may allow me to hook the PDP to my serial-to-wifi board.