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SCN2681T

Dual asynchronous receiver/transmitter (DUART)

Philips Electronics 

Philips Semiconductors

Dual asynchronous receiver/transmitter (DUART)

Product specification

SCN2681T

DESCRIPTION

The Philips Semiconductors SCN2681 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 SCN2681T features a faster bus cycle time than the

standard SCN2681. 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 SCN2681T

interfaces directly with microprocessors and may be used in a polled

or interrupt driven system.

The operating mode and data format of each channel can be

programmed independently. Additionally, each receiver and

transmitter can select its operating speed as 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 DUART particularly

attractive for dual-speed channel applications such as clustered

terminal systems.

Each receiver is quadruple buffered to minimize the potential of

receiver over-run or to reduce interrupt overhead in interrupt driven

systems. In addition, a flow control capability is provided to disable

a remote DUART transmitter when the receiver buffer is full.

Also provided on the SCN2681T are a multipurpose 7-bit input port

and a multipurpose 8-bit output port. These can be used as general

purpose I/O ports or can be assigned specific functions (such as

clock inputs or status/interrupt outputs) under program control.

For a complete functional description and programming information

for the SCN2681T, refer to the SCN2681 product specification.

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 115.2k baud

– Non-standard rates to 115.2

– Non-standard user-defined rate derived from programmable

counter/timer

– 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 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

– 100kΩ typical pull-up resistors

• Multi-function 8-bit output port

– Individual bit set/reset capability

– Outputs can be programmed to be status/interrupt signals

• 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:

1X – 1MB/sec transmitter and receiver; 16X – 500kB/sec receiver

and 250kB/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 +5V power supply

• Commercial and industrial temperature ranges available

ORDERING INFORMATION

DESCRIPTION

40-Pin Plastic Dual In-Line Package (600mil-wide DIP)

VCC = +5V +10%, TA = 0°C to +70°C

SCN2681TC1N40

44-Pin Plastic Lead Chip Carrier (PLCC)

SCN2681TC1A44

NOTE: For a full register description and programming information see the SCN2681.

DWG #

SOT129-1

SOT187-2

1998 Sep 04

2

853–1002 19970

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