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TMS320F280049C: SCI cant get to 921600 Baud with SysClk 100Mhz

Alan Grimmer
Intellectual 290 points
Part Number: TMS320F280049C


Hi,

I'm having troubles getting comms going.

With SYS_CLK set to 100Mhz I can only achieve around 1025000 or 785000 baud . not 921600.

based on "divider = ((lspclkHz  / (baud * 8U)) - 1U)"

We require 921600 for backwards compatibility with our PC applications.

I'm looking to change the SYS_CLK to 90Mhz where it will happily do 921600 baud. 

But it feels like such a waste. Is there another way to maintain 100Mhz and 921600 baud?

Alan

10Mhz * 20 / 2 
  • 0
    TI__Guru 60865 points

    Hi Alan,

    I do think you do need to change the SYSCLK to get a closer baud rate.

    How about SYSCLK = LSPCLK = 96MHz, BRR = 12, Actual Baud = 923077 (+0.16%)

    • X1 = 16MHz, PLL = x12 / 2

    Or SYCLK = LSPLK = 97.28MHz, BRR = 12, Actual Baud = 935285 (+1.5%)

    • X1 = 10.24MHz, PLL  = x19 / 2
  • 0 in reply to Devin Cottier
    Intellectual 290 points
    The one that failed for me was SYCLK =100Mhz LSPLK =25Mhz Baud =921600

    Both those suggestions worked for me when adjusted to use the internal 10Mhz source.

    I then tried SYCLK =100Mhz LSPLK =100Mhz Baud =921600 and this works for me

    Thank you for your help, is there any downside to running LSPLK at SYCLK 1:1 ?
  • 0 in reply to Alan Grimmer
    TI__Guru 60865 points
    Hi Alan,

    Running the LSPCLK faster will probably result in very slightly higher power dissipation. Otherwise you just want to make sure LSPCLK isn't any higher than whatever the datasheet specifies (see Table 5-18. Internal Clock Frequencies) - in this case the max is 100MHz so it isn't really possible to exceed the specification (but other C2000 devices with a faster max SYSCLK could have a LSPCLK limit lower than the max SYSCLK frequency).

    Keep in mind that the INTOSC has a frequency tolerance that is quite a bit looser than you'd get from an external XTAL and this will affect your overall baud tolerance. See the datasheet Table 5-23. INTOSC Characteristics.