Dual Universal Asynchronous Receiver/Transmitter (DUART)

The 28L202 is a high performance dual UART. Its functional and programming features closely match but greatly extend those of previous Philips dual channel UARTs. Its configuration on power up is similar that of the SC26C92. Its differences from the SC26C92 are: 256-character receiver, 256 character transmit FIFOs, 3 V and 5 V compatibility, 8 I/O ports for each UART-16 total, arbitrating interrupt system and overall faster bus and data speeds. It is fabricated in an advanced 0.5 micron CMOS process. It is a member of the IMPACT^® line of data communications parts.

Pin programming will allow the device to operate with either the Motorola or Intel bus interface by changing the function of some pins (reset is inverted, DACKN and IACKN enabled for example).

The Philips Semiconductors 28L202 Dual Universal Asynchronous Receiver/Transmitter (DUART) is a single-chip CMOS-LSI communications device that provides two full-duplex asynchronous receiver/transmitter channels in a single package. It interfaces directly with microprocessors and may be used in a polled or interrupt driven system. The use of the Interrupt system provides intelligent interrupt vectors.

The operating mode and data format of each channel may be programmed independently. Additionally, each receiver and transmitter can select its operating speed as one of 27 fixed baud rates; a 16x clock derived from one of two programmable counter/timers 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 DUART particularly attractive for dual-speed channel applications such as clustered terminal systems and bridges.

Each receiver and transmitter is buffered by 256 character FIFOs to nearly eliminate the potential of receiver overrun, transmitter underrun and to reduce interrupt overhead in interrupt driven systems. In addition, a flow control capability (Xon/Xoff and RTS/CTS) is provided to disable a remote transmitter when the receiver buffer is full.

Also provided on the 28L202 is a multipurpose 8-bit I/O for each channel. These can be used as general-purpose I/O ports or can be assigned specific functions (such as clock inputs or status and interrupt outputs) under program control. Normally they will be used for modem control and DMA interface. All ports have change of state detectors and input sections are always active making output signals available to the internal circuits and the control processor.

The 28L202 is available in a 52-pin TSSOP package. For other package options, contact Philips.