Hi priyan george,
About the higher level in the MCU, you can find it in the KL25 datasheet.
http://www.nxp.com/files/32bit/doc/data_sheet/KL25P80M48SF0.pdf?fasp=1&WT_TYPE=Data%20Sheets&WT_VEND...
The input high voltage:

The output high level:

Wish it helps you!
If you still have question, please contact me!
Have a great day,
Kerry
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