Table 18-1. SCG modes of operation (continued)
Mode
Description
Information regarding SOSC operation during normal and low power stop modes is found in the
.
Slow Internal Reference
Clock (SIRC)
Slow Internal Reference Clock (SIRC) mode is entered when all the following conditions occur:
• RUN MODE: 0010 is written to RCCR[SCS].
VLRUN MODE: 0010 is written to VCCR[SCS] and 1 is written to SIRCCSR[SIRCLPEN].
• SIRCEN = 1
• SIRCVLD = 1
In SIRC mode, SCGCLKOUT and system clocks are derived from the slow internal reference clock.
Two frequency ranges are available for SIRC clock as described in the SIRCCFG[RANGE] register
definition. Changes to SIRC range settings will be ignored when SIRC clock is enabled.
Information regarding SIRC operation during normal and low power stop modes is found in the
.
Fast Internal Reference
Clock (FIRC)
Fast Internal Reference Clock (FIRC) mode is the default clock mode of operation and is entered
when all the following conditions occur:
• RUN MODE: 0011 is written to RCCR[SCS].
VLRUN MODE: Invalid mode. Programming SCG into FIRC mode will be ingored.
• FIRCEN = 1
• FIRCVLD = 1
In FIRC mode, SCGCLKOUT and system clocks are derived from the fast internal reference clock.
Four frequency range settings are available for FIRC clock as described in the FIRC[RANGE]
register definition. Changes to FIRC range settings will be ignored when FIRC clock is enabled.
Information regarding FIRC operation during normal and low power stop modes is found in the
.
Low Power FLL
(LPFLL)
Low Power FLL (LPFLL) mode is entered when all the following conditions occur:
• RUN MODE: 0101 is written to RCCR[SCS].
VLRUN MODE: Invalid mode. Programming SCG into LPFLL mode will be ingored.
• LPFLLEN = 1
• LPFLLVLD = 1
In LPFLL mode, SCGCLKOUT and system clocks are derived from the Low Power FLL (LPFLL). By
default the LPFLL will be running in open-loop mode using default trim values. In closed-loop mode
(LPFLLTREN=1 and LPFLLTRUP=1) LPFLL will be auto trimmed using a selectable reference clock
as specified by its corresponding SCG_LPFLLTCFG[TRIMSRC]. The LPFLL will lock its frequency
to the LPFLL factor, as specified by the SCG_LPFLLCFG[FSEL].
Information regarding LPFLL operation during normal and low power stop modes is found in the
"Stop" row of this table
.
Stop
Entered whenever the MCU enters a Stop state. The power modes are chip specific. For power
mode assignments, see the chapter that describes how modules are configured and SCG behaviour
during Stop recovery. Entering Stop mode, all SCG clock signals are static except the following
clocks which can continue to run and stay enabled in the following cases:
SIRCCLK is available in Normal Stop and VLPS mode when all the following conditions become
true:
Chapter 18 System Clock Generator (SCG)
Kinetis KE1xZ256 Sub-Family Reference Manual, Rev. 3, 07/2018
NXP Semiconductors
403
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