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NXP Semiconductors

FS26

Safety system basis chip with low power for ASIL D/ASIL B

19.4.2 Calibration procedure

The calibration procedure consists of activating the counter for a specific duration and comparing the result with

the MCU's accurate clock and timing. Once the timer expires, the MCU reads back its final value to compare

with its own accurate time of activation and to calculate a time offset.

NXP recommends performing the calibration between -20 °C and 85 °C. Calibration example:

• Select the timer function 1 and set the after run value to 65535 (~32 s).

• Start the counter.

• Read the counter when the MCU RTC reaches 20 s (must be less than 30 s with ±5.0 % oscillator accuracy).

• If the oscillator period is at exact typical value (absolutely no deviation error), expected reading is 40960.

• The exact reading calculates the error correction factor ECF = exact_reading/expected_reading.

• ECF < 1 if the oscillator is faster than the exact typical value.

• ECF > 1 if the oscillator is slower than the exact typical value.

• After calibration, the new after run or wake-up values to set the counter are "after run x ECF" and "wake-up x

ECF".

19.4.3 LDT functions

LDT_FNCT[2:0]

Long Duration Timer Function

Function 1: In normal mode, count and generate a flag or an interrupt when the counter

reaches the after run value.

Function 2: In normal mode, count until the counter reaches the after run value and enters

Low-power mode.

Function 3: In normal mode, count until the counter reaches the after run value and enters

low power mode. Once in Low-power mode, count until the counter reaches the wake-up

value or until another wake-up event occurs, and wakes up.

Function 4: In Low-power mode, count until the counter reaches the wake-up value or

until another wake-up event occurs, and wakes up.

Function 5: In Low-power mode, count and do not wake up unless the counter overflow

occurs or if the device wakes up by another wake-up input source.

Table 125. Long Duration Timer functions

FS26_SDS

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Product short data sheet

Rev. 6.0 — 12 December 2025

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FS26 Datenblatt(PDF) 127 Page - NXP Semiconductors