The commands to modify the simulated parameters are sent from a PC over an RS-232 line to the peripheral device. A microcontroller containing a UART receives these commands as 8-bit frames and processes the data. After processing, the microcontroller uses its I/O port bits to send data to the parameter generation hardware. The parameter's signal is modified as specified by the down-loaded command. The modified signals are then output to the patient monitor to produce the appropriate visual displays.