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UM10850
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User manual
Rev. 2.4 — 13 September 2016
76 of 464
NXP Semiconductors
UM10850
Chapter 4: LPC5410x System configuration (SYSCON)
The frequency measurement function circuit is able to measure the target frequency with
an error of less than 0.1%, provided the reference frequency is precisely known.
Uncertainty in the reference clock (for example the +/- 1% accuracy of the IRC) will add to
the measurement error of the target clock. In general, though, this additional error is less
than the uncertainty of the reference clock.
There can also be a modest loss of accuracy if the reference frequency exceeds the
target frequency by a very large margin (25x or more). Accuracy is not a simple function of
the magnitude of the frequency difference, however. Nearly identical frequency
combinations, still with a spread of about 43x, result in errors of less than 0.05%.
If the target and reference clocks are different by more than a factor of approximately
500, then the accuracy decreases to +/- 4%.