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TMDXLCDK6748: What means each CLKMODE posible value?

Juan Encinas
Intellectual 510 points
Part Number: TMDXLCDK6748
Other Parts Discussed in Thread: TMS320C6748

Hi

I am using the TMS320C6748 development kit.

Could you tell me which are the differences between CLKMODE = 0 and CLKMODE 1 because looking at the data sheet

 

Then there are examples of an On-Chip oscillator 

And an internal oscillator

So the point is that taking a look at the dev kit schematic

It seems to be using an exterenal oscillator (Comparing with the previous figures) but if a use CLKMODE = 0, what means On-Chip oscillator instead of CLKMODE = 1 (External oscillator) it Works properly

So i don't know if i am misunderstanding the date sheet, if there is an internal oscillator inside the TMS320C6748 that generate the clock instead of the IC os the last figure or if that IC is working as the On-Chip oscillator.

Could you please explain me the CLKMODEs, which circuit is what and why the DEV KIT Works using On-Chip oscillator?

Thanks in advance,

Juan 

  • 0
    TI__Guru**** 393215 points
    Hi Juan,

    What the CLKMODE bit actually does is to control the internal oscillator inverting buffer (connected between OSCIN and OSCOUT on figure 6-6). Let's discuss the two settings:

    CLKMODE=0: In this use case the buffer is enabled and it uses the crystal X1 to generate the clock. In this use case an external oscillator is NOT connected to OSCIN.

    CLKMODE = 1: In this use case the buffer is disabled and an external 1.2V oscillator is connected to OSCIN, as on the EVM board. In this use case a crystal X1 is NOT connected between OSCIN and OSCOUT.

    As you have seen the second use case will also work with CLKMODE=0, because OSCIN is directly connected to the PLL input, however:
    1. There will be some power loss from the active oscillator inverting buffer.
    2.The inverted clock will be driven on OSCOUT, which will emit unnecessary noise in the system.