Abstract: A Communication Interface Box (CIB) enables bidirectional synchronous/asynchronous data transfer between external devices including data terminal equipment (DTE) and data communication equipment (DCE) and a personal computer by way of the parallel port of the personal computer. The CIB provides one or more input/output ports from the DCE and DTE for receiving or transmitting serial data. A bidirectional universal synchronous/asynchronous transmitter/receiver USART and a control circuit are used to transfer control and data signals between external devices and a personal computer for serial data analysis. The CIB eliminates the need for equipment dedicated solely to serial data analysis as well as the need to add hardware boards to personal computers to perform serial data analysis. The CIB allows for serial data analysis by way of the parallel port of a personal computer.