Aliasing VCP Baud Rates - FTDI

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Document Reference No.: FT_000161 Aliasing VCP Baud Rates Application Note AN_120 Version 1.0 Clearance No.: FTDI# 122 - change the 34,00,00,00 entry to 03,80,00,00 (simple as both of the values are available from the previous list) To alias a rate of 197k baud to the standard 4,800 baud menu option under windows : - find the best divisor, check that it is sufficiently accurate and then modify the appropriate INF file entry. 3000000/197,000 = 15.228. The best divisor is 15.25. 3000000/15.25 = 196,721. 196,721/197,000 = 99.8%. This is well within the required 3% tolerance. Set bits 16:15:14 to 010 for a sub-integer divisor of 0.25, and the lower bits to 0F. - replace the 71,02,00,00 entry with 0F,80,00,00. Incorporating these two changes the FTDIPORT.INF entry becomes FtdiPort232.NT.HW.AddReg] HKR,,ConfigData,1,11,00,3F,3F,10,27,00,00,88,13,00,00,C4,09,00,00,E2,04,00,00,0F,80,00,00,38 ,41,00,00,9C,80,00,00,4E,C0,00,00,03,80,00,00,1A,00,00,00,0D,00,00,00,06,40,00,00,03,80,00,00 ,00,00,00,00,D0,80,00,00 Copyright © 2009 Future Technology Devices International Limited 9
Document Reference No.: FT_000161 Aliasing VCP Baud Rates Application Note AN_120 Version 1.0 Clearance No.: FTDI# 122 4.4 Aliasing the FT2232H and FT4232H for Baud Rates up to 12MBaud The instructions in section 4.3 are still applicable for the FT2232H and the FT4232H up to 3MBaud. The calculations for sub integers still apply. To alias baud rates between 3MBaud and 12MBaud it is necessary to use driver version 2.4.20 or later and the most significant bit (MSB) of the divisor must be a 1. This will ensure the divisor is dividing a 12MHz clock and not a 3MHz clock. Example: Each field consists of 4 bytes, ordered as follows: Byte0, Byte1, Byte2, Byte3. Bits 13 through 0 denote the integer divisor while bits 16, 15 and 14 denote the sub-integer divisor, as follows 16,15,14 = 000 - sub-integer divisor = 0 16,15,14 = 001 - sub-integer divisor = 0.5 16,15,14 = 010 - sub-integer divisor = 0.25 16,15,14 = 011 - sub-integer divisor = 0.125 16,15,14 = 100 - sub-integer divisor = 0.375 16,15,14 = 101 - sub-integer divisor = 0.625 16,15,14 = 110 - sub-integer divisor = 0.75 16,15,14 = 111 - sub-integer divisor = 0.875 The following lists the standard values and their respective baud rates. 10,27,00,80 => divisor = 10000, rate = 1,200 88,13,00,80 => divisor = 5000, rate = 2,400 C4,09,00,80 => divisor = 2500, rate = 4,800 E2,04,00,80 => divisor = 1250, rate = 9,600 71,02,00,80 => divisor = 625, rate = 19200 38,41,00,80 => divisor = 312.5, rate = 38,400 9C,80,00,80 => divisor = 156, rate = 76,923 4E,C0,00,80 => divisor = 78, rate = 153,846 34,00,00,80 => divisor = 52, rate = 230,769 1A,00,00,80 => divisor = 26, rate = 461,538 0D,00,00,80 => divisor = 13, rate = 923,077 06,40,00,80 => divisor = 6.5, rate = 153,846 03,80,00,80 => divisor = 3.25, rate = 3,692,308 00,00,00,80 => RESERVED D0,80,00,80 => divisor = 208.25, rate = 57,623 To alias a rate of 38400 baud to the standard 300 baud menu option under windows: - change the 10,27,00,00 entry to 38,41,00,80 (simple as both of the values are available from the previous list) To alias a rate of 8.5M baud to the standard 4,800 baud menu option under windows: - find the best divisor, check that it is sufficiently accurate and then modify the appropriate INF file entry. 12000000/8,500,000 = 1.41. The best divisor is 1.375. 12000000/1.375 = 8,727,273. 8,727,273/8,5000,000 = 102.6%. This is just within the required 3% tolerance. Set bits 16:15:14 to 100 for a sub-integer divisor of 0.375, and the lower bits to 01. Copyright © 2009 Future Technology Devices International Limited 10
Page 1 and 2: Future Technology Devices Internati
Page 3 and 4: 1 Introduction Document Reference N
Page 5 and 6: 3 Baud Rate Calculation Document Re
Page 7 and 8: 4.2 Aliasing Using the Original Sub
Page 9: 4.3 Aliasing Using the Additional S
Page 13 and 14: 5 Contact Information Head Office -
Page 15 and 16: Appendix A - FTDIPORT.INF Example D
Page 17 and 18: AddReg=FtdiPort232.NT.HW.AddReg [Ft

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