17.8.6 32kHz External Crystal Oscillator (XOSC32K) Control

Name: XOSC32K
Offset: 0x14
Reset: 0x0080
Property: Write-Protected

Bit 15141312111098 
    WRTLOCK STARTUP[2:0] 
Access R/WR/WR/WR/W 
Reset 0000 
Bit 76543210 
 ONDEMANDRUNSTDBYAAMPEN EN32KXTALENENABLE  
Access R/WR/WR/WR/WR/WR/W 
Reset 100000 

Bit 12 – WRTLOCK Write Lock

This bit locks the XOSC32K register for future writes to fix the XOSC32K configuration.

ValueDescription
0The XOSC32K configuration is not locked.
1The XOSC32K configuration is locked.

Bits 10:8 – STARTUP[2:0] Oscillator Start-Up Time

These bits select the start-up time for the oscillator.

The OSCULP32K oscillator is used to clock the start-up counter.

Table 17-6. Start-Up Time for 32kHz External Crystal Oscillator
STARTUP[2:0] Number of OSCULP32K Clock CyclesNumber of XOSC32K Clock CyclesApproximate Equivalent Time
(OSCULP = 32kHz)(1)(2)(3)
0x013122μs
0x13231068μs
0x22048362592μs
0x340963125092μs
0x4163843500092μs
0x53276831000092μs
0x66553632000092μs
0x713107234000092μs

Notes: 1. Number of cycles for the start-up counter.

2. Number of cycles for the synchronization delay, before PCLKSR.XOSC32KRDY is set.

3. Start-up time is n OSCULP32K cycles + 3 XOSC32K cycles.

Bit 7 – ONDEMAND On Demand Control

The On Demand operation mode allows an oscillator to be enabled or disabled depending on peripheral clock requests.

In On Demand operation mode, i.e., if the ONDEMAND bit has been previously written to one, the oscillator will only be running when requested by a peripheral. If there is no peripheral requesting the oscillator s clock source, the oscillator will be in a disabled state.

If On Demand is disabled the oscillator will always be running when enabled.

In standby sleep mode, the On Demand operation is still active if the XOSC32K.RUNSTDBY bit is one. If XOSC32K.RUNSTDBY is zero, the oscillator is disabled.

ValueDescription
0The oscillator is always on, if enabled.
1The oscillator is enabled when a peripheral is requesting the oscillator to be used as a clock source. The oscillator is disabled if no peripheral is requesting the clock source.

Bit 6 – RUNSTDBY Run in Standby

This bit controls how the XOSC32K behaves during standby sleep mode:

ValueDescription
0The oscillator is disabled in standby sleep mode.
1The oscillator is not stopped in standby sleep mode. If XOSC32K.ONDEMAND is one, the clock source will be running when a peripheral is requesting the clock. If XOSC32K.ONDEMAND is zero, the clock source will always be running in standby sleep mode.

Bit 5 – AAMPEN Automatic Amplitude Control Enable

ValueDescription
0The automatic amplitude control for the crystal oscillator is disabled.
1The automatic amplitude control for the crystal oscillator is enabled.

Bit 3 – EN32K 32kHz Output Enable

ValueDescription
0The 32kHz output is disabled.
1The 32kHz output is enabled.

Bit 2 – XTALEN Crystal Oscillator Enable

This bit controls the connections between the I/O pads and the external clock or crystal oscillator:

ValueDescription
0External clock connected on XIN32. XOUT32 can be used as general-purpose I/O.
1Crystal connected to XIN32/XOUT32.

Bit 1 – ENABLE Oscillator Enable

ValueDescription
0The oscillator is disabled.
1The oscillator is enabled.