DESCRIPTION
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. Each receiver is buffered with eight character FIFOs (first-in-first-out memories) and one shift register to minimize the potential for receiver overrun and to reduce interrupt overhead in interrupt driven systems. In addition, a handshaking capability is provided to disable a remote UART transmitter when the receiver buffer is full. (RTS control) The 28C94 provides a power-down mode in which the oscillator is stopped and the register contents are stored. This results in reduced power consumption on the order of several magnitudes.
NXP Semiconductors
