AM625: AM625:Cannot find the `CTRLMMR_WKUP_LFXOSC_TRIM` register

Hello Ryan,

Please give me 1-2 days to find more information regarding your topic.

Thank you for your patience!

Best Regards,

Borislav Lazarkov

Hello Ryan,

Could you please try the MCU_CTRL_MMR_CFG0_LFXOSC_TRIM register and report the observation after using it?

The register is in the AM62x TRM in section 14.2.1.1.2.2.114 MCU_CTRL_MMR_CFG0_LFXOSC_TRIM Register.

Best Regards,

Borislav Lazarkov

If this register changes the capacitance value, will it change automatically? Or do we need to configure it according to the capacitance value?

If I change the capacitor value, will the register change automatically? Or do I need to set it according to the capacitor value?

Hello Ryan,

The register does not change automatically, it must be manually configured based on the crystal load capacitance (CL) used on the PCB.

The LFXOSC_TRIM register controls the AGC (Automatic Gain Control) amplifier current multiplication gain ([18:16] LFXOSC_TRIM_I_MULT). This is not an auto-tuning mechanism, it is a static trim setting that the user must set according to the crystal's CL specification. The hardware has no mechanism to sense the external capacitance and adjust automatically.

As stated in the AM625 datasheet in section 6.12.4.1.3 WKUP_LFOSC0 Internal Oscillator Clock Source:

• Crystal Load Capacitance (CL) 6 pF to 9.5 pF- [18:16] i_mult value 3b'001 (4x AMP_AGC IBIAS)
• Crystal Load Capacitance (CL) 8.5 pF to 12 pF- [18:16] i_mult value 3b'010 (5x AMP_AGC IBIAS) — Default

The default reset value of this field is 3b'010, which corresponds to the 8.5 pF to 12 pF range. If your crystal falls within this range, no change is needed. If it falls in the 6 pF to 9.5 pF range, you must write 3b'001 to [18:16].

Best Regards,

Borislav Lazarkov

If I need to write to the register manually, how do I know that writing to the MCU_CTRL_MMR_CFG0_LFXOSC_TRIM register is the right choice, and not WKUP's?

Hello Ryan,

Please check the schematic, look at which ball/pin the 32.768 kHz crystal is connected to on the AM625 device. Cross-reference the ball name in the AM625 datasheet pin function table. To which ball is connected- to the WKUP_LFOSC0_XI/XO or to the MCU_LFOSC0_XI/XO?

Best Regards,

Borislav Lazarkov

The chip pin connected to WKUP, but there's no WKUP register

Hello Ryan,

I spoke with my colleagues regarding your topic.

Please use the MCU_CTRL_MMR_CFG0_LFXOSC_TRIM register. 

The registers are set during power cycle and this should not be a concern.

Best Regards,

Borislav Lazarkov