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NXP Semiconductors

FS6500-FS4500-ASILD

Safety power system basis chip with CAN FD and LIN transceivers

aaa-037783

32 kHz

OSC

30 s

488 s

(calibration)

1.0 s (cal: 488 s)

PRESCALER 1

(/16)

24-bit COUNTER

PRESCALER 2

(/2048)

EXTERNAL

INT

MISO

MOSI

SCLK

CSB

to internal:

mode change

(LPOFF, WU)

16 bits: AFTER RUN

24 bits: WAKE UP

CONTROL REGISTER

READ

COMP.

Figure 54. Long duration timer block diagram

12.8.1 Timer characteristics

In normal operation, the timer can count up to 194 days, with 1 second resolution. In calibration mode, the

prescaler 2 is bypassed and the timer can count up to 2.28 hours, with 488 µs resolution. The calibration

principle consists in activation of the counter for a dedicated and accurate duration, due to the MCU accurate

clock and timing. The MCU then reads back the timer count, compares the count versus the accurate time of

activation, then calculates a time offset. It is recommended to perform the calibration between -20 °C and +85

°C.

Osc freq

Osc period

Prescaler

Counter

resolution

Max count

Operation

32768 Hz

30.52 μs

16 x 2048

1 s

4660 Hrs

194 days

Calibration

32768 Hz

30.52 μs

488 µs

8192 s

2.28 Hrs

Table 13. Long duration timer characteristics

12.8.2 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.

FS6500-FS4500-ASILD

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Product data sheet

Rev. 8 — 5 August 2024

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