The PC87108A is a serial communications device with infrared capability. It supports 6 modes of operation and is backward compatible with the 16550 and 16450. The operational modes are: UART, Sharp-IR, IrDA 1.0 SIR, IrDA 1.1 MIR and FIR, and Consumer Electronics IR (also referred to as TV Remote or Consumer Remote Control). The device provides two methods to allow its internal registers to be accessed. It can either directly decode a 16-bit address, or it can accept an externally generated chip select in combination with a 4-bit address. When a 16-bit address is used, any one of four PC COMM port legacy addresses can be selected as the base address. In order to support existing legacy software based upon the 16550 UART, the PC87108A provides a special fallback mechanism that automatically switches the device to 16550 compatibility mode when the baud generator divisor is accessed through the legacy ports in bank 1. The device architecture has been optimized to meet the requirements of a variety of UART and infrared based applications. DMA support for all operational modes has been incorporated into the architecture. Routing for interrupt and DMA handshake signals is provided to meet Plug-and-Play as well as PC' 95 requirements.