12.5.6 Internal High-Frequency Oscillator Frequency Tune

Name:	OSCHFTUNE
Offset:	0x09
Reset:	0x0
Property:	-


Bit	7	6	5	4	3	2	1	0
	TUNE[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	0

Bits 7:0 – TUNE[7:0] Frequency Tuning Value

This bit field controls the manual tuning of the output frequency of the Internal High-Frequency Oscillator (OSCHF). The frequency can be tuned 32 steps down or 31 steps up from the oscillator’s target frequency. Thus, the register’s acceptable input value range is -32 to +31.

Writing to bits 6 and 7 has no effect, as bit 5 is mirrored to bits 6 and 7 due to the 6-bit value in this bit field being represented in signed (two’s complement) form.

Note:

The TUNE value is locked when the Auto-Tune Enable (AUTOTUNE) bit in the Internal High-Frequency Oscillator Control A (CLKCTRL.OSCHFCTRLA) register is enabled. The TUNE register is updated with the latest tune value when AUTOTUNE is disabled.

After AUTOTUNE is disabled, there is a delay before the TUNE register is updated. This delay depends on the system clock frequency. The delay consists of a fixed auto-tune logic delay (0.75 µs) and three system clock cycles:

20 MHz system clock: t_UPD = 0.75 µs + 3 * 0.05 µs = 0.90 µs
5 MHz system clock: t_UPD = 0.75 µs + 3 * 0.20 µs = 1.35 µs