MAX32665-MAX32668 User Guide
Maxim Integrated Page 52 of 457
4.1.1 Oscillator Inplementation
Before using any oscillator, the desired oscillator must first be enabled by setting the oscillator’s enable bit in the
GCR_CLK_CTRL register. Once an oscillator’s enable bit is set, the oscillator’s ready bit must read 1 prior to attempting to
use the oscillator as a system oscillator source. The oscillator ready status flags are contained in the GCR_CLK_CTRL register.
Once the corresponding oscillator ready bit is set, the oscillator can then be selected as SYS_OSC by configuring the Clock
Source Select field (GCR_CLK_CTRL.sysosc_sel).
Any time firmware changes SYS_OSC by changing GCR_CLK_CTRL.sysosc_sel, the Clock Ready bit GCR_CLK_CTRL.sysosc_rdy
is automatically cleared to indicate that a SYS_OSC switchover is in progress. When switchover is complete,
GCR_CLK_CTRL.sysosc_rdy is set to 1 by hardware indicating the oscillator selected is ready for use.
4.1.2 96MHz Internal Main High-Speed Oscillator
The devices are available with a 96MHz internal high-speed oscillator. This is the fastest oscillator and draws the most
power.
This oscillator is also used by the USB PHY, Audio subsystem, and the SDHC. If the USB or SDHC or Audio subsytem is
enabled, the 96MHz oscillator must be enabled, independent of the selection of SYS_OSC.
Optionally, this oscillator can be powered down automatically when in DEEPSLEEP mode by setting register bit
GCR_PMR.hircmmpd.
4.1.3 60MHz Low Power Internal Oscillator
This is a low-power internal oscillator that can be selected as SYS_OSC. This oscillator is automatically selected as SYS_OSC
after a System Reset or POR. This oscillator is also the dedicated clock for the TPU. If the TPU is enabled, the 60MHz internal
oscillator must be enabled, independent of the selection of SYS_OSC. When used as the TPU clock it can be divided by 2.
4.1.4 32MHz Bluetooth Radio Oscillator
This is the oscillator that directly drives the Bluetooth radio. It can also be selected as SYS_OSC. It is important to use the
correct capacitor values on the PCB when connecting the crystal. Figure 4-2 depicts the method to determine the capacitor
values C
LIN
and C
LOUT.
In order to enable this oscillator, the Bluetooth LDOs must be enabled by setting the
GCR_BTLE_LDOCR.ldorxen, GCR_BTLE_LDOCR.ldotxen, GCR_BTLE_LDOCR.ldorxvsel, GCR_BTLE_LDOCR.ldotxvsel register
fields.
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