DESCRIPTION
The Philips Semiconductors SCC2681 Dual Universal Asynchronous Receiver/Transmitter (DUART) is a single-chip MOS-LSI communications device that provides two independent full-duplex asynchronous receiver/transmitter channels in a single package. The SCC2681T features a faster bus cycle time than the standard SCC2681. The quick bus cycle eliminates or reduces the need for wait states with fast CPUs and permits high throughput in I/O intensive systems. Higher external clock rates may be used with the transmitter, receiver and counter timer which in turn provide greater versatility in baud rate generation. The SCC2681T interfaces directly with microprocessors and may be used in a polled or interrupt driven system. It is manufactured in CMOS technology.

FEATURES
• Fast bus cycle times reduce or eliminate CPU wait states
• Dual full-duplex asynchronous receiver/transmitters
• Quadruple buffered receiver data registers
• Programmable data format
    – 5 to 8 data bits plus parity
    – Odd, even, no parity or force parity
    – 1, 1.5 or 2 stop bits programmable in 1/16-bit increments
• 16-bit programmable Counter/Timer
• Programmable baud rate for each receiver and transmitter selectable from:
    – 22 fixed rates: 50 to 115.2 k baud
    – Non-standard rates to 115.2
    – Non-standard user-defined rate derived from programmable counter/timer
    – External 1× or 16× clock
• Parity, framing, and overrun error detection
• False start bit detection
• Line break detection and generation
• Programmable channel mode
    – Normal (full-duplex)
    – Automatic echo
    – Local loopback
    – Remote loopback
• Multi-function programmable 16-bit counter/timer
• Multi-function 7-bit input port
    – Can serve as clock or control inputs
    – Change of state detection on four inputs
    – 100 kΩ typical pull-up resistors
• Multi-function 8-bit output port
    – Individual bit set/reset capability
    – Outputs can be programmed to be status/interrupt/DMA signals
    – Auto 485 turn-around
• Versatile interrupt system
    – Single interrupt output with eight maskable interrupting conditions
    – Output port can be configured to provide a total of up to six separate wire-ORable interrupt outputs
• Maximum data transfer rates:
    – 1× – 1 MB/sec transmitter and receiver
    – 16× – 500 kB/sec receiver and 250 kB/sec transmitter
• Automatic wake-up mode for multidrop applications
• Start-end break interrupt/status
• Detects break which originates in the middle of a character
• On-chip crystal oscillator
• Single +5 V power supply
• Commercial temperature range