DESCRIPTION
The 28C94 quad universal asynchronous receiver/transmitter (QUART) combines four enhanced Philips Semiconductors industry-standard UARTs with an innovative interrupt scheme that can vastly minimize host processor overhead. It is implemented using Philips Semiconductors’ high-speed CMOS process that combines small die size and cost with low power consumption. The operating speed of each receiver and transmitter can be selected independently at one of eighteen fixed baud rates, a 16X clock derived from a programmable counter/timer, or an external 1X or 16X clock. The baud rate generator and counter/timer can operate directly from a crystal or from external clock inputs. The ability to independently program the operating speed of the receiver and transmitter make the QUART particularly attractive for dual-speed channel applications such as clustered terminal systems.

FEATURES
• New low overhead interrupt control
• All commercial parts meet industrial timing and temperature parameters
• Four Philips Semiconductors industry-standard UARTs
• Eight byte receive FIFO and eight byte transmit FIFO for each UART
• 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
• Baud rate for the receiver and transmitter selectable from:
   – 23 fixed rates: 50 to 230.4K baud; Non-standard rates to 1.0 M baud
   – User-defined rates from the programmable counter/timer associated with each of two blocks
   – External 1x or 16x 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 loop back, remote loopback
• Programmable interrupt priorities
• Identification of highest priority interrupt
• Global interrupt register set provides data from interrupting channel
• Vectored interrupts with programmable vector format
• IACKN and programmable DTACKN signals
• Built-in baud rate generator with choice of 18 rates
• Four I/O pins per UART for modem controls, clocks, etc.
• Power down mode
• High-speed CMOS technology
• 52-pin PLCC package
• Commercial and industrial temperature ranges available
• On-chip crystal oscillator
• TTL compatible
• Single +5V power supply with low power mode
• Two multifunction programmable 16-bit counter/timers
• 1MHz 16x mode operation
• 10ns data bus release time
• “Watch Dog” timer for each receiver