Hi Gene, I figured out my problem. I cut and pasted the stimulus file from the HELP-->MPLAB Help menu. I searched on simulator Stimulus and the chose Pin Stimulus. The first line in the example is: ! Stimulus file for SAMPLE.ASM STEP RB7 RB6 RB5 RB4 RB3 RB2 RB1 RB0 ! PortB Pins 3 0 0 0 0 1 0 0 1 ! 9 x 5 What I needed was to change the names of the port pins to: ! Stimulus file for SAMPLE.ASM STEP GP5 GP4 GP3 GP2 GP1 GP0 ! PortB Pins 3 0 0 0 0 1 0 ! 9 x 5 All works find now. - -Mark Date: Tue, 25 Nov 1997 08:28:37 -0500 From: Gene Norris I have had recent experience in this area and thanks to past postings I was able to get it to work. The example I was following is in the MPLAB manual on page 67. At least for the windows version of MPSIM it is wrong. I found that if I left out the "Pins" line the example would work. Hope this helps, Gene.