The ST16C554/554D (554) is a quad Universal Asynchronous Receiver and Transmitter (UART) with 16 bytes of transmit and receive FIFOs, selectable receive FIFO trigger levels and data rates of up to 1.5 Mbps. Each UART has a set of registers that provide the user with operating status and control, receiver error indications, and modem serial interface controls. An internal loopback capability allows onboard diagnostics. The 554 is available in a 64-pin LQFP and a 68-pin PLCC package. The 64-pin package only offers the 16 mode interface, but the 68-pin package offers an additional 68 mode interface which allows easy integration with Motorola processors. The ST16C554CQ64 (64-pin) offers three