STM32F4 OSC Problem

[Scarlet]

Hi everyone

I'm currently using the NUCLEO-F429ZI development board. I'm planning to create a PCB using the STM32F429ZIT6, but I've encountered some questions during the planning stage.

1. According to the datasheet, HSE_OSC is specified to provide 8MHz, and CubeIDE also indicates "Input Freq HSE = 8MHz." However, on the NUCLEO-F429ZI development board, the JFVNY 25.000 oscillator supplies 25MHz. I have verified that the SPI clock indeed derives from multiplying and dividing an 8MHz source, but when I measure the JFVNY 25.000 oscillator on the development board, it does indeed supply 25MHz. Why are these two frequencies inconsistent, or am I misunderstanding something?
2. Referring to the Clock tree and considering, if not using the RTC section, is it possible to omit providing the external LSE_OSE?

[Tesla DeLorean]

Sure that's not driving the Ethernet PHY?

I might check the schematic later.

Check the EVAL or DISCO boards, the might use a 25 MHz clock.

[Scarlet]

I think I misunderstood. In the UM1974 User Manual, it states that "JFVNY 25.000" is the X4 oscillator. Although it doesn't specify what part of the oscillation it provides, the document indicates that X3 is the HSE oscillator.

[Andrew Neil]

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@Scarlet wrote:

In the UM1974 User Manual, it states that "JFVNY 25.000" is the X4 oscillator. 

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Does it?

I don't see "JFVNY" mentioned anywhere in that document:

I also don't see "X4" anywhere.

That's Rev 10 (Aug 2023) - What revisions of board & manual do you have?

[Andrew Neil]

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@Scarlet wrote:

1. According to the datasheet, HSE_OSC is specified to provide 8MHz, ?

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That'll be when it's used as an oscillator - with an external crystal.

 

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@Scarlet wrote:

1. However, on the NUCLEO-F429ZI development board, the JFVNY 25.000 oscillator supplies 25MHz?

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There you're using an external oscillator, and just feeding a clock signal into the chip - bypassing the chip's own HSE oscillator.

 

EDIT:

The datasheet actually says that the HSE Oscillator can do 4-26 MHz:

 

With an external oscillator - ie, bypassing HSE - the clock input can be 1-50 MHz:

 

 

 

[Scarlet]

Yes, I saw in the datasheet that it states "the HSE Oscillator can do 4-26 MHz."

To avoid affecting other timing, I'll start with setting the input HSE to 8MHz as indicated in the IDE. I'll further study the external oscillator section.

Although I have high-speed requirements, I'm currently limited by the SPI maximum timing of 45MHz. I'm not sure if an external oscillator can help me increase the speed.

Thank you very much.

[mƎALLEm]

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Although I have high-speed requirements, I'm currently limited by the SPI maximum timing of 45MHz. I'm not sure if an external oscillator can help me increase the speed.

PLL is there to do that. No need to increase the Crystal frequency to boost the one of the system.

[mƎALLEm]

Hello,

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1. According to the datasheet, HSE_OSC is specified to provide 8MHz,

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Could you please indicate the page or a screenshot of the page? 8MHz could be generated by the STLink MCO and used in BYPASS mode from your target MCU.

As stated by @Andrew Neil the datasheet indicates that HSE could be in the range of 4-26MHz.

1. However, on the NUCLEO-F429ZI development board, the JFVNY 25.000 oscillator supplies 25MHz. I have verified that the SPI clock indeed derives from multiplying and dividing an 8MHz source, but when I measure the JFVNY 25.000 oscillator on the development board, it does indeed supply 25MHz.

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According to the schematics there is no even the crystal PCB footprint on the board of the HSE. Could you please tell us which from which reference you did conclude this information. Could it be X3 (the crystal used for the ethernet PHY?

 

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Referring to the Clock tree and considering, if not using the RTC section, is it possible to omit providing the external LSE_OSE?

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Yes and you can use PC14(OSC32_IN) and PC15(OSC32_OUT) as GPIOs if you remove R37 and R38.

 

Edit: "no even the crystal PCB footprint on the board of the HSE" Yes it does but no restriction to populate it with 25MHz crystal.

[Scarlet]

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Could you please indicate the page or a screenshot of the page?

 

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I found the "Input Freq HSE 8MHz" setting in the CubeIDE Clock Config. I don't have the development environment at hand currently, but I'll provide a screenshot of the source later.

 

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8MHz could be generated by the STLink MCO and used in BYPASS mode from your target MCU.

So I can use STLink to program the microcontroller without providing an external oscillator externally?

However, the MCU requires an HSE of 8MHz for execution. Right?

 

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According to the schematics there is no even the crystal PCB footprint on the board of the HSE. Could you please tell us which from which reference you did conclude this information. Could it be X3 (the crystal used for the ethernet PHY?

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Yes, I mistook X4 for the HSE OSC. I found in the UM1974 User Manual that X3 is the HSE OSC. However, I'm still unclear about the meaning of 'not provided'. 

 

[Andrew Neil]

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@Scarlet wrote:

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So I can use STLink to program the microcontroller without providing an external oscillator externally?

However, the MCU requires an HSE of 8MHz for execution. Right?

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The MCU doesn't require HSE at all.

HSE is just one of the many potential clock sources.

The default for the board is to bypass the HSE, and use the 8MHz clock signal provided by the ST-Link