PR2 = 2083U
makes TIMER2 trigger every 2083 CPU cycles. Calculating
52.083 us / 2083 = 25 ns
1 / 25 ns = 40 MHz
we can conclude that the processor is probably running at FCY = 40 MHz
in the example.
The letter u
in PR2 = 2038u;
does not mean microseconds; it is a C language syntax that makes the integer literal unsigned. See Signedness (Wikipedia).