The ST16C1550, ST16C1551 series (here on denoted as the 155X) is a universal asynchronous receiver and transmitter (UART). The 155X is an improved version of the SSI 73M1550 and SSI 73M2550 UART with higher operating speed and lower access time. The 155X provides enhanced UART functions with 16 byte FIFOs, a modem control interface, independent programmable baud rate generators with clock rates 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 loopback capability allows onboard diagnostics. The 155X is available in a 28-pin PLCC/plastic-DIP, 48-pin TQFP packages.. The Baud rate generator can be configured for either crystal or external clock input with the exception of the 28 pin 1551 package. An external clock must be provided for the 28 pin 1551 package. Each package type, with the exception of the 28 pin 1550, provides a buffered reset output that can be controlled through user software. DMA monitor signals TXRDY/RXRDY are not available at the 155X I/O pins but these signals are accessible through ISR register bits 4-5. Except as listed above, each package version has the same features. The 155X is functionally compatible with the 16C550. The 155X is fabricated in an advanced CMOS process to achieve low drain power and high speed requirements.