I'm using MPLAB 4.12.12, and wrote a demo program for a 12c509a for the first time. The program makes a one-chip crystal controlled sq. wave oscillator by using 4 GPIO pins (GP0=output, GP1,GP2,GP3=input). I arranged for the GP1:GP2:GP3 set to select one of eight frequencies (1/10 Hz, 1, 10, 100, 1k, 10k, 100kHz) based on input values 000 - 111. In order to test the program (which also switches dynamically between frequencies when inputs are changed), I need to use a pin stimulus file. I wrote the following sample ("sqwave.sti"): !12.28.99 23.15 SQWAVE.STI !stimulus file for SQWAVE.ASM CYCLE GPIO1 GPIO2 GPIO3 1 1 0 0 2 1 1 1 3 0 1 1 4 0 0 1 5 0 0 0 6 1 0 0 7 0 1 0 8 1 0 0 9 1 1 1 10 0 1 0 20 1 0 0 30 0 1 0 100 1 1 1 1000 0 0 0 I reset the program in MPLAB and enabled the pin stimulus file. But when I run MPLAB step-by-step, the GPIO register stays at b'0000100x' instead of matching the stimulus pin values I wanted. What am I missing? I went ahead and burned the eprom, and the circuit works exactly as intended. So there's nothing wrong with the inputs in real life. Any suggestions? This has to be a simple fix. ================================================================ Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: ral@lcfltd.com Least Cost Formulations, Ltd. URL: http://lcfltd.com/ 824 Timberlake Drive Tel: 757-467-0954 Virginia Beach, VA 23464-3239 Fax: 757-467-2947 "Vere scire est per causae scire" ================================================================