I added HALT mode into simulation - if any instructions from range 0x80...0x87 is executed (these are placeholders for future RET and RST n) then processor is HALT until user pressed GO button (on the left side of simulation):
It may help to run large test program when result of every sub-test is displayed on 7-segment indicators with following HALT and when user checked the result he/she may press GO button to run to the next sub-test and so on.
Logisim simulation file was updated: nedonand.circ
P.S. This behavior will still be available even in future full-scale NEDONAND when RET instruction is called from the main program (return stack is empty in this case)