17.8.9 8MHz Internal Oscillator (OSC8M) Control

Name: OSC8M
Offset: 0x20
Reset: 0xXXXX0382
Property: Write-Protected

Bit 3130292827262524 
 FRANGE[1:0]  CALIB[11:8] 
Access R/WR/WR/WR/WR/WR/W 
Reset xx0000 
Bit 2322212019181716 
 CALIB[7:0] 
Access R/WR/WR/WR/WR/WR/WR/WR/W 
Reset 0000000x 
Bit 15141312111098 
       PRESC[1:0] 
Access R/WR/W 
Reset 11 
Bit 76543210 
 ONDEMANDRUNSTDBY    ENABLE  
Access R/WR/WR/W 
Reset 101 

Bits 31:30 – FRANGE[1:0] Oscillator Frequency Range

These bits control the oscillator frequency range according to the table below. These bits are loaded from Flash Calibration at startup.

FRANGE[1:0]Description
0x04 to 6MHz
0x16 to 8MHz
0x28 to 11MHz
0x311 to 15MHz

Bits 27:16 – CALIB[11:0] Oscillator Calibration

These bits control the oscillator calibration. The calibration field is split in two:

CALIB[11:6] is for temperature calibration

CALIB[5:0] is for overall process calibration

These bits are loaded from Flash Calibration at startup.

Bits 9:8 – PRESC[1:0] Oscillator Prescaler

These bits select the oscillator prescaler factor setting according to the table below.

PRESC[1:0]Description
0x01
0x12
0x24
0x38

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 OSC8M.RUNSTDBY bit is one. If OSC8M.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 OSC8M behaves during standby sleep mode:

ValueDescription
0The oscillator is disabled in standby sleep mode.
1The oscillator is not stopped in standby sleep mode. If OSC8M.ONDEMAND is one, the clock source will be running when a peripheral is requesting the clock. If OSC8M.ONDEMAND is zero, the clock source will always be running in standby sleep mode.

Bit 1 – ENABLE Oscillator Enable

The user must ensure that the OSC8M is fully disabled before enabling it, and that the OSC8M is fully enabled before disabling it by reading OSC8M.ENABLE.

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