IMX7ULPCEC datasheet(23/118 Pages) NXP

23 / 118 page

2.3 External clock sources

In normal functional mode, this device operates off two primary external reference

clocks: System oscillator clock (SOSC) and RTC oscillator clock (ROSC):

• System oscillator clock is a high frequency reference clock with a frequency in

the range of 16 MHz to 32 MHz. This clock is used as a reference clock to the on-

chip PLLs which generate all the required high frequency clocks.

• RTC oscillator clock is the 32.768 kHz constant frequency, real-time clock.

2.4 Oscillators

The system oscillator, in conjunction with an external crystal or resonator, generates a

reference clock for the device. The system oscillator module supports 16-32 MHz

crystals or resonators. It also provides the option for an external input clock to

EXTAL signal directly.

The RTC oscillator is in the VBAT domain. The RTC oscillator module, in

conjunction with an external crystal, generates a 32.768 kHz real-time reference clock

for the RTC and will always be enabled and supplying clock to SRTC. This is the

default clock source.

2.5 Internal clock sources

This device is capable of generating these internal reference clocks:

• The FIRC is the fast IRC clock with nominal frequency in the range from 48 to 60

MHz. In addition, the FIRC provides a clock selection option for peripherals.

• The SIRC is the slow IRC clock with nominal frequency of 16 MHz. The SIRC

provides a clock selection option for peripherals.

• The IRC1K generates 1 kHz clock that is enabled in all modes of operation,

including all low power modes.

• The RTC OSC has the capability to provide nominal 32 kHz (not recommended

for accurate clock and normal operation) IRC in absence of the external OSC

reference clock if the VBAT domain is enabled.

NOTE

The internal oscillator is automatically multiplexed in the

clocking system when the system detects a loss of clock.

The internal oscillator will provide clocks to the same on-

Clocking

i.MX 7ULP Applications Processor—Consumer Products, Rev. 0, 06/2019

NXP Semiconductors

IMX7ULPCEC Datasheet(PDF) 23 Page - NXP Semiconductors