Most often I build small 'emulators' that use a microcontroller and an EPROM. Using a PC parallel port should work just fine. You need to monitor the DEVICE COMMAND flag from the I/O board. At power up, or following a PRESET operation, DEVICE COMMAND will be asserted, and the PC or emulator should pre-clock the interface DEVICE FLAG input to clear this 'false' request. Once pre-clocked, eash assertion of DEVICE COMMAND should be followed by sending the 8-bit parallel data, then strobing DEVICE FLAG. A correct load will halt with 102077 in the S-register. If your directly connecting the PC to the HP, be careful about ground loops and latchup issues if both devices are not powered up at the same moment. If you need to power the emulator up seperately from the HP I'd reccomend some form of isolation. Dwight K. Elvey wrote: