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?

[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).

[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?

[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]

Really helpful comment! ​

I will go over them!

Have a good day :D