Hello, I need to simulate a 360 bit serial data stream on RB0 on my 16F84, so I wrote a Visual C++ program which would produce my .sti file for me. It produces a file with 360 lines of the format specified in the MPSIM help file: CYCLE RB0 [ElapsedCycle][Pin status] ... etc. The text file looked ok when I opened it in MPLAB (I didn't look very closely :-), so I tried to use it. Next thing, "Invalid Page Fault" appeared, MPLAB closed, followed very shortly after by KERNEL32. After a PC reset, I tried again, and the same thing happened. I looked at the file again and discovered that Visual C++ (obviously not my code you understand ;-) had put an 'X' at the end of the file. When I removed the 'X' and went to try again, the Debug > Simulator Stimulus option was greyed out. My questions are: a) Was it the 'X' at the end of the file which caused MPLAB (...and my PC) to bomb? or was I asking too much for it to simulate (the last simulator cycle (number 360) in the file was 33950 ). b) How do I re-enable the Debug > Simulator Stimulus option again? (I've got the development mode set to MPSIM, and I can step through the code) TIA for any help you boys and girls can offer me. Steve