17.8.9 8MHz Internal Oscillator (OSC8M) Control
| Name: | OSC8M |
| Offset: | 0x20 |
| Reset: | 0xXXXX0382 |
| Property: | Write-Protected |
| Bit | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | |
| FRANGE[1:0] | CALIB[11:8] | ||||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | |||
| Reset | x | x | 0 | 0 | 0 | 0 | |||
| Bit | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | |
| CALIB[7:0] | |||||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | R/W | R/W | |
| Reset | 0 | 0 | 0 | 0 | 0 | 0 | 0 | x | |
| Bit | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | |
| PRESC[1:0] | |||||||||
| Access | R/W | R/W | |||||||
| Reset | 1 | 1 | |||||||
| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
| ONDEMAND | RUNSTDBY | ENABLE | |||||||
| Access | R/W | R/W | R/W | ||||||
| Reset | 1 | 0 | 1 |
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 |
|---|---|
| 0x0 | 4 to 6MHz |
| 0x1 | 6 to 8MHz |
| 0x2 | 8 to 11MHz |
| 0x3 | 11 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 |
|---|---|
| 0x0 | 1 |
| 0x1 | 2 |
| 0x2 | 4 |
| 0x3 | 8 |
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.
| Value | Description |
|---|---|
| 0 | The oscillator is always on, if enabled. |
| 1 | The 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:
| Value | Description |
|---|---|
| 0 | The oscillator is disabled in standby sleep mode. |
| 1 | The 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.
| Value | Description |
|---|---|
| 0 | The oscillator is disabled or being enabled. |
| 1 | The oscillator is enabled or being disabled. |