SCN2681 datasheet(18/30 Pages) PHILIPS

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Philips Semiconductors

Product specification

SCN2681

Dual asynchronous receiver/transmitter (DUART)

1998 Sep 04

Table 3.

Bit Rate Generator Characteristics Crystal or Clock = 3.6864MHz

NORMAL RATE (BAUD)

ACTUAL 16x CLOCK (kHz)

ERROR (%)

0.8

1.2

110

1.759

-0.069

134.5

2.153

0.059

150

2.4

200

3.2

300

4.8

600

9.6

1050

16.756

-0.260

1200

19.2

1800

28.8

2000

32.056

0.175

2400

38.4

4800

76.8

7200

115.2

9600

153.6

14.4K

230.4

19.2k

307.2

28.8K

460.8

38.4k

614.4

57.6K

921.6

115.2K

1843.2K

NOTE: Duty cycle of 16x clock is 50%

± 1%.

Asynchronous UART communications can tolerate frequency error

of 4.1% to 6.7% in a “clean” communications channel. The percent

of error changes as the character length changes. The above

percentages range from 5 bits not parity to 8 bits with parity and one

stop bit. The error with 8 bits no parity and one stop bit is 4.6%. If a

stop bit length of 9/16 is used, the error tolerance will approach 0

due to a variable error of up to 1/16 bit time in receiver clock phase

alignment to the start bit.

Table 4.

ACR 6:4 Field Definition

ACR 6:4

MODE

CLOCK SOURCE

000

Counter

External (IP2)

001

Counter

TxCA – 1x clock of Channel A transmitter

010

Counter

TxCB – 1x clock of Channel B transmitter

011

Counter

Crystal or external clock (x1/CLK) divided by 16

100

Timer (square wave)

External (IP2)

101

Timer (square wave)

External (IP2) divided by 16

110

Timer (square wave)

Crystal or external clock (x1/CLK)

111

Timer (square wave)

Crystal or external clock (x1/CLK) divided by 16

NOTE: Timer mode generates a squarewave.

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