I am using MPSIM with a stimulus file which changes pins 4 and 5 on PortB (PIC16C64). I am trying (desperately) to cause a Change on PortB interrupt to happen. When the pins change value, the interrupt (at org 0x04) is not called. I can see that INTCON changes though. Does MPSIM simulate this interrupt or am I just wishing? If it does, obviously I have some code problems. This is my first attempt at using this interrupt. I thought I followed AN566 (Using the PortB Int. on Change as an...) and AN552 (Implementing Wake-up on Key Stroke) pretty closely. What am I forgetting? If anyone has sample code (bare bones) that does this, could you please share it. Thanks alot in advance. DRC