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数据搜索系统，热门电子元器件搜索 |
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HT68FU50 数据表(PDF) 191 Page - Holtek Semiconductor Inc |
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HT68FU50 数据表(HTML) 191 Page - Holtek Semiconductor Inc |
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191 / 244 page  HT68F20/HT68F30/HT68F40/HT68F50/HT68F60 HT68FU30/HT68FU40/HT68FU50/HT68FU60 Rev. 1.50 191 March 15, 2011 Baud Rate Generator To setup the speed of the serial data communication, the UART function contains its own dedicated baud rate generator. The baud rate is controlled by its own internal free running 8-bit timer, the period of which is deter- mined by two factors. The first of these is the value placed in the baud rate register BRG and the second is the value of the BRGH bit with the control register UCR2. The BRGH bit decides if the baud rate generator is to be used in a high speed mode or low speed mode, which in turn determines the formula that is used to cal- culate the baud rate. The value N in the BRG register which is used in the following baud rate calculation for- mula determines the division factor. Note that N is the decimal value placed in the BRG register and has a range of between 0 and 255. UCR2 BRGH Bit 0 1 Baud Rate (BR) f [64 (N+1)] CLKI f [16 (N+1)] CLKI By programming the BRGH bit which allows selection of the related formula and programming the required value in the BRG register, the required baud rate can be setup. Note that because the actual baud rate is deter- mined using a discrete value, N, placed in the BRG reg- ister, there will be an error associated between the actual and requested value. The following example shows how the BRG register value N and the error value can be calculated. · Calculating the baud rate and error values For a clock frequency of 4MHz, and with BRGH set to ²0² determine the BRG register value N, the actual baud rate and the error value for a desired baud rate of 4800. From the above table the desired baud rate BR = f [64 (N+1)] CLKI Re-arranging this equation gives N = f (BRx64) CLKI - 1 Giving a value for N = 4000000 4800 64 () x - 1 = 12.0208 To obtain the closest value, a decimal value of 12 should be placed into the BRG register. This gives an actual or calculated baud rate value of BR= 4000000 [64(12+1)] = 4808 Therefore the error is equal to = 0.16% 4 8 0 8 - 4 8 0 0 4 8 0 0 The following tables show the actual values of baud rate and error values for the two value of BRGH. Baud Rate K/BPS Baud Rates for BRGH=0 fCLKI=4MHz fCLKI=3.579545MHz fCLKI=7.159MHz BRG Kbaud Error (%) BRG Kbaud Error (%) BRG Kbaud Error (%) 0.3 207 0.300 0.16 185 0.300 0.00 ¾¾¾ 1.2 51 1.202 0.16 46 1.190 -0.83 92 1.203 0.23 2.4 25 2.404 0.16 22 2.432 1.32 46 2.380 -0.83 4.8 12 4.808 0.16 11 4.661 -2.90 22 4.863 1.32 9.6 6 8.929 -6.99 5 9.321 -2.90 11 9.322 -2.90 19.2 2 20.833 8.51 2 18.643 -2.90 5 18.643 -2.90 38.4 ¾¾¾¾¾¾ 2 32.286 -2.90 57.6 0 62.500 8.51 0 55.930 -2.90 1 55.930 -2.90 115.2 ¾¾¾¾¾¾ 0 111.859 -2.90 Baud Rates and Error Values for BRGH = 0 |
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