Hi Barbara Moraes,
Thank you for your interest in NXP Semiconductor products and for the opportunity to serve you.
The OSRVAL value is the number of BRG clocks used to receive one data bit (Fig 1) and I think you can learn the FCLK in the 13.3.1 Configure the USART clock and baud rate, it's very clear (Fig 2).
Fig 1
Fig 2
Have a great day,
TIC
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