I have a circuit based on AT89C52 (from ATMEL) with an RS232 connector to a host computer. I couldn't find a software simulator to single-step through the bit-receiving interrupt handler. I suspect that my firmware (15,000 lines of assembly source code) messes up some bits received from the RS232 connector.

I have heard of a software simulator UMPS which lets the user create a "stimuli" file, a file containing the data to be sent from the host computer to my AT89C52. Once the simulation starts, the user can click a button to start pushing each bit from the stimuli to the AT89C52, and AT89C52 would get a serial interrupt and process the bit. I want to step through this simulation.

I couldn't get UMPS to work.

By the way, any hardware emulator that helps my debug this interrupt handler and other interrupt handlers please?