Abstract: A computer system implements a standard modem without the use of a microcontroller. Instead, a digital signal processor is provided on an expansion card, but with direct links to the computer system itself. The code usually implemented in the microcontroller is instead implemented as a virtual modem controller to be called by the operating system of the computer itself. Further, this virtual modem controller includes a virtualized UART, that appears to the operating system software as a hardware UART, and the operating system driver software need not even have its input and output instructions replaced. Instead, debug registers are provided as breakpoints whenever an input/output instruction is executed to the I/O port range at which the UART would normally appear.