FT260 HID-CLASS USB TO UART/I2C BRIDGE IC
Version 1.1
Document No.: FT_001272 Clearance No.: FTDI#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.
푶풑풆풓풂풕풊풏품 푪풍풐풄풌 푭풓풆풒풖풆풏풄풚
퐁퐚퐮퐝 퐑퐚퐭퐞 =
푩풂풖풅 푫풊풗풊풔풐풓
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.
ퟒퟖ푴푯풛
퐁퐚퐮퐝 퐃퐢퐯퐢퐬퐨퐫 =
= ퟒퟏퟔ. ퟔퟔퟕ
ퟏퟏퟓퟐퟎퟎ푯풛
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
Ideal
Actual
Actual
Baud
Baud Rate
Baud Divisor
Baud Divisor
Baud Rate
Error Rate
0.00%±0.25%*Note
0.00%±0.25%
0.00%±0.25%
0.00%±0.25%
0.00%±0.25%
0.00%±0.25%
0.00%±0.25%
0.00%±0.25%
0.16%±0.25%
0.04%±0.25%
0.04%±0.25%
0.01%±0.25%
0.01%±0.25%
0.00%±0.25%
0.00%±0.25%
0.00%±0.25%
12,000,000
9,600,000
8,000,000
6,000,000
3,000,000
2,000,000
1,500,000
1,000,000
921,600
460,800
230,400
115,200
57,600
4
5
4
5
12,000,000
9,600,000
8,000,000
6,000,000
3,000,000
2,000,000
1,500,000
1,000,000
923,076.9231
460,984.3938
230,492.1969
115,211.5212
57,605.7606
38,400
6
6
8
8
16
24
32
48
16
24
32
48
52
52.083
104.16
208. 3
416. 6
833. 3
1,250
2,500
5,000
104.125
208.250
416.625
833.250
1250
2500
5000
38,400
19,200
19,200
9,600
9,600
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