FT260 datasheet(21/58 Pages) FTDI

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FT260 HID-CLASS USB TO UART/I2C BRIDGE IC

Version 1.0

Doc ument N o.: FT _001272 C learance N o.: FT DI#484

5.3

UART Interface

A universal asynchronous receiver/transmitter (UART) is a computer hardware device that translates data

between parallel and serial forms. UARTs are commonly used in conjunction with communication

standards such as TIA (formerly EIA) RS-232, RS-422 or RS-485.

The UART can support baud rates from 1.2 Kbaud to 12 Mbaud defined by the following function.

�� =

��

The baud divisor is used to divide the operating clock frequency to the desired baud rate. It can take any

value between 4 and 40000 with the added option of adding a fractional component in the order of

1/8ths.

Example: To generate an 115200 baud rate in the FT260, the operating clock frequency to the UART

controller equals to 48MHz. The baud divisor can be calculated as shown in the below equation.

�� =

��

= ��. ��

Due to the fractional component is the order of 1/8ths, the baud divisor must be selected as 416.625. It

is obvious that the difference of baud divisors will produce a percentage error. A comparison of standard

baud rates and the divisor values can be seen in Table 5.3 below. This shows the baud rate required,

followed by the divisor value needed to achieve this if the UART is running off a 48MHz clock. Then it lists

the actual baud rate achieved and finally the percentage error this produces.

Target

Baud Rate

Ideal

Baud Divisor

Actual

Baud Divisor

Actual

Baud Rate

Baud

Error Rate

12,000,000

0.00%±0.25%*Note

9,600,000

0.00%±0.25%

8,000,000

0.00%±0.25%

6,000,000

0.00%±0.25%

3,000,000

0.00%±0.25%

2,000,000

0.00%±0.25%

1,500,000

0.00%±0.25%

1,000,000

0.00%±0.25%

921,600

52.083

923,076.9231

0.16%±0.25%

460,800

104.16

104.125

460,984.3938

0.04%±0.25%

230,400

208. 3

208.250

230,492.1969

0.04%±0.25%

115,200

416. 6

416.625

115,211.5212

0.01%±0.25%

57,600

833. 3

833.250

57,605.7606

0.01%±0.25%

38,400

1,250

1250

38,400

0.00%±0.25%

19,200

2,500

2500

19,200

0.00%±0.25%

9,600

5,000

5000

9,600

0.00%±0.25%

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