STM32L432KC HSE (external clock source) without using MCO from ST-Link

[J.Yun]

Hello,

I would like to ask you one question.

In the datasheet of NUCLEO-L432KC, MCO output from ST-Link MCU should be used for input clock of L432KC MCU to use/enable HSE option.

I wonder if I can use HSE without using MCO output from ST-LINK MCU.

I want to connect external XTAL for HSE option, but there is only clock_input pin on L432KC (there's no clock_output pin for HSE).

Thank you in advance for your reply.

[berendi]

If it's not in the datasheet, then it's not possible. What do you need it for?

[waclawek.jan]

You can't use a crystal, but you can connect a crystal oscillator such as https://global.kyocera.com/prdct/electro/product/crystal-device/clock/ or similar from any other manufacturer.

You'd need to disconnect MCO from CK_IN, of course.

JW

[J.Yun]

I would appreciate if you could explain the difference between XTAL and crystal oscillator you mentioned.

I think they are same, Isn't it?

[J.Yun]

Just curiosity.

In the datasheet, I can get a more precise frequency if I use 8 MHz XTAL (MCO from ST-LINK).

I am working on frequency-related project, so I just want to improve the freq. accuracy.

If it is impossible, I have no choice but to change the MCU to G431KB that uses HSE clock.

[J.Yun]

Or I can add additional circuit for HSE in my customized PCB layout.

1. 8MHz XTAL driving circuit.
2. Readout circuit (its output will replace the MCO output from ST-LINK MCU).

[berendi]

It's possible to improve the accuracy of HSI by calibrating it to LSE. TIM15 or TIM16 capture channels can be connected to the LSE clock, and you can play with the HSITRIM value to adjust HSI speed in small steps. See Internal/external clock measurement with TIM15/TIM16 in the reference manual.

[waclawek.jan]

The terminology is confusing, I know.

Crystal as a part is a passive two-terminal device (even if it is packaged in four-pin package, especially SMD crystals are). They need to be connected into a circuit, and this circuit (and this is the confusion) is then called crystal oscillator.

Crystal oscillator as a part is an active device with at least three pins - ground, power supply and output - usually packaged in four pin package, whether it's through-hole or SMD, and it generates a digital-level signal of a specified frequency without any other external circuitry. Sometimes the fourth pin is active and acts as an enable/output gate. Sometimes these are marked as XO or SXO (for Simple Crystal Oscillator); then there are derivatives of these with added value, such as VCXO (Voltage Controlled XO) or TCXO (Temperature Compensated XO).

JW

[J.Yun]

Thanks for your kind reply.

I will play!​

Have a good day!

[J.Yun]

Really helpful comment! ​

I will go over them!

Have a good day :D