The ST16C2552 (2552) is a dual universal asynchronous receiver and transmitter (UART). The ST16C2552 is an improved version of the NS16C552 UART. The 2552 provides enhanced UART functions with 16 byte FIFOs, a modem control interface, and data rates up to 1.5 Mbps. Onboard status registers provide the user with error indications and operational status. System interrupts and modem control features may be tailored by external software to meet specific user requirements. An internal loop-back capability allows onboard diagnostics. Independent programmable baud rate generators are provided to select transmit and receive clock rates from 50 Bps to 1.5 Mbps. The Baud rate generator can be configured for either crystal or external clock input. The 2552 is available in 44, pin PLCC packages. The 2552 provides block mode data transfers (DMA) through FIFO controls. DMA transfer monitoring is provided through the signals -TXRDY and -RXRDY. An Alternate Function Register provides the user with the ability to the write the control registers for both UARTS concurrently. The 2552 is functionally compatible with the NS16C552. The 2552 is fabricated in an advanced CMOS process to achieve low drain power and high speed requirements.