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SCC2681T

Dual asynchronous receiver/transmitter (DUART)

Philips Electronics 

Philips Semiconductors

Dual asynchronous receiver/transmitter (DUART)

Product data

SCC2681T

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.

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 16× clock derived from a programmable counter/timer,

or an external 1× or 16× 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 SCC2681T 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 SCC2681T, refer to the SCC2681 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 115.2 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

ORDERING INFORMATION

DESCRIPTION

44-Pin Plastic Lead Chip Carrier (PLCC)

VCC = +5 V ± 10%, Tamb = 0 °C to +70 °C

SCC2681TC1A44

NOTE: For a full register description and programming information see the SCC2681.

DWG #

SOT187-2

2004 Apr 06

2

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