LMK61E2: Will reserved bit in the register ignore coorsponding bit in byte writing? How to chose an optimal value for XO_CAPCTRL?

wallace liu

Part Number: LMK61E2

Hi Experts,

LMK61E2 has reserved bits in its registers. Most reserved bits have the same default value of 0, a few have the value of 1, e.g. R35.[1:0]. If we execute a I2C communication and use a byte to overwrite a specific writeable register, how should we make the bit value which is in same position in the byte as the one in the register, the default value or any value?

The datasheet mentions little on the XO Margining Offset Value(R16 and R17) . The LMK61xx Oscillator Programming Tool has a input entry to modify the load capacitor value. What is the upper/lower bound of the XO_CAPCTRL value, 0~2047? Do you have any formula to correlate this XO_CAPCTRL value and the offset of out frequency? Do we need a spectrum analyzer to verify such frequency fine turning does happen?

Best Regards!

Wallace

over 4 years ago

0 Hao Z over 4 years ago

TI__Mastermind 18070 points

Hi Wallace,

For reserved bits, please follow default / reset values (they mean the same).

It is difficult to map XO_CAPCTRL values to actual output frequency because this relationship is dependent on too many variables, such as PCB parasitic capacitance. The recommended way of doing this is to fine tune this register and observe the output frequency on a frequency counter until the desired frequency is generated. Spectrum analyzer and oscilloscope are not accurate enough in terms of frequency measurement.

Regards,
Hao

0 wallace liu over 4 years ago in reply to Hao Z

Intellectual 280 points

Hello Hao,

Your answer is well understood and thank you!

Wallace

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LMK61E2: Will reserved bit in the register ignore coorsponding bit in byte writing? How to chose an optimal value for XO_CAPCTRL?