The 754C is a quad universal asynchronous receiver transmitter (UART) with 64-byte
FIFOs, automatic hardware and software flow control, and data rates up to 3 Mbps. It incorporates
the functionality of four UARTs, each UART having its own register set and FIFOs. The four UARTs
share only the data bus interface and clock source, otherwise they operate independently. Another
name for the UART function is Asynchronous Communications Element (ACE), and these terms are used
interchangeably. The bulk of this document describes the behavior of each ACE, with the
understanding that four such devices are incorporated into the 754C. The 754C offers enhanced
features. It has a transmission control register (TCR) that stores received FIFO threshold level to
start or stop transmission during hardware and software flow control. With the FIFO RDY register,
the software gets the status of TXRDY/RXRDY for all four ports in one access. On-chip status
registers provide the user with error indications, operational status, and modem interface control.
System interrupts may be tailored to meet user requirements. An internal loopback capability allows
Each UART transmits data sent to it from the peripheral 8-bit bus on the TX signal and
receives characters on the RX signal. Characters can be programmed to be 5, 6, 7, or 8 bits. The
UART has a 64-byte receive FIFO and transmit FIFO and can be programmed to interrupt at different
trigger levels. The UART generates its own desired baud rate based upon a programmable divisor and
its input clock. It can transmit even, odd, or no parity and 1-, 1.5-, or 2-stop bits. The receiver
can detect break, idle or framing errors, FIFO overflow, and parity errors. The transmitter can
detect FIFO underflow. The UART also contains a software interface for modem control operations,
and software flow control and hardware flow control capabilities.
The 754C is available in a 64-pin TQFP PM package. RXRDY and
TXRDY functionality is not supported in the TL16C754CPM device.