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TMS320F28020: Datasheet spec's 40MHz, but measures 50MHz?

Robin Vice
Intellectual 950 points
Part Number: TMS320F28020
Other Parts Discussed in Thread: C2000WARE, TMS320F28027

Hi All,

The math to set up I2C and SCI clock rates hasn't been working quite right.  When I select a value, the data rates are a little higher than anticipated.  I just want to make sure I understand correctly.

The datasheet (SPRS523P rev Feb 2021) for TMS320F28020DAT shows that this particular part is 40MHz (see 28020 column of Table 6-1).

When I enable XCLKOUT on GPIO18, I see 50MHz on the scope, with SYSCTRL::XCLK set to 2 (div by 1).  With it set to 0 (div by 4), I get 12.5MHz.

Here's an image of the shipping label:

Can you help me understand this?

Thanks,
robin

  • +1
    TI__Guru 71785 points

    Robin,

    Even though the device is only guaranteed to work up to 40MHz, there is nothing that prevents you from using a PLLCR value that exceeds this.  I think that you may be running an example that was has the PLLCR value for another device in this family(F28022 I think) that is spec'd at 50MHz.

    For 40MHz, assuming you are using the internal oscillator(10MHz), you need to change the PLLCR value to 4(from 5). 

    If this is happening from a C2000Ware example that is built for this specific device, please let me know so we can file a bug against this example

    Best,

    Matthew

  • 0 in reply to MatthewPate
    Intellectual 950 points

    Of course (face palm)!

    It's been a while since I started this project, and I don't remember all the details, but it probably started life as example code on the LaucnXL-F2802x, which is running a TMS320F28027 probably at 60MHz.  I'm not sure how I got to 50MHz, but your comment about PLLCR is spot on.

    Thanks for your help.