; This rot13 thing actually runs on the bare metal.  No operating 
; system, you'd most likely assemble this to a list file (listing
; all the compiled opcodes) and then manually <d>eposit the resultant
; code to the PDP-11 from the Console ROM controller.  
        .TITLE rot13kungfu
LOOP1:
; 177560 is the address for the Console Controller Ready flag.  If it
; tstb's to be true, then there's a character waiting for us.
        MOV @#177560, R0
        TSTB R0
        BMI LOOP2
; no key, go back and test again.
        BR LOOP1
LOOP2:
; aha! A key doth wait.  Transfer what's in the inbuffer to register 0.
        MOV @#177562, R0
; Add 15 (that's 015, remember.  Octal and all that) to the character read 
; in.
	ADD 15, R0
; and then write the new value to the terminal output buffer, brazenly
; not testing to see if it's ready for the byte.
        MOV R0, @#177566
; lather; rinse; repeat.
        BR LOOP1
        .END