TMS320F28335 XINTF maximum frequency

Hi Ali,

The highest the frequency that XCLKOUT can be is SYSCLKOUT (which can be higher than 25MHz) - XCLKOUT is brought out on a dedicated pin. See table 6-37 in the 28335 datasheet to see some examples of possible XCLKOUT timing configurations. XCLKOUT isn't all there is to XINTF access timing though if that is more what you are looking for. For more timing information you should see section 6.14 of the datasheet, because other factors than XCLKOUT come into play - you need to make sure you have the correct lead, active, and trail wait-states set according to whatever device you are accessing over your XINTF and according to the minimum settings specified in the datasheet. Note: there is no internal hardware to detect invalid lead/active/trail settings.

I hope this helps clarify things.

Regards,

Katie

Ali,

To add to Katie's comment, the buffer limitation does exists for XINTF usage as well. It is not that the pin will fail to toggle above 25MHz, it is just that there is a spec of 8ns rise time and an 8ns fall time which doesn't change with frequency. This means that at 25MHz, 40% of the signal period is switching time. The signal will only be high or low for 30% of the time. This will get worse as you move above 25MHz. If the application can handle it then it will work.

Regards,
Dave Foley