You might try looking at the M9312 proms that Don North has made available here: http://www.ak6dn.com/PDP-11/M9312/
If you have an M9312 in your system it will have the basic console prom in it. There are listings of the prom contents on that web page. There is also a simple diagnostic prom that loops forever near the bottom of the page. If you don't have an M9312 then you could probably key in a program from the rom listings provided. I'd bet Don will be along shortly to provide a better explanation.
