Bad edges of SCK signal on SPI interface

[ASham.3]

Hi all
I am using STM32F303VGT6 and initialize SPI1 as Master. My microcontroller supports SPI frequency up to 18 MHz. But at 9 MHz, SCK signal is already triangle waveform, while MOSI signal is normal waveform. SCK pin is initialized with GPIO_SPEED_FREQ_HIGH and GPIO_MODE_AF_PP, without pull-up or pull-down.

My electrical circuit does not contain any components that increase the capacitance of the circuit.

The attached images show the MOSI (top) and SCK (bottom) signals. The first image contains a frequency of 18 MHz, the second contains a frequency of 9 MHz. Although the SCK frequency is always higher than MOSI, the quality of the SCK signal at the equivalent frequency is lower.

Is there a solution to this problem?

  

[AScha.3 · Accepted solution]

Hi,

> Is there a solution to this problem?

1. Correct measurement : set probe to 10:1 .

2. Set pin speed : high .

[ASham.3]

The pin speed is already "high".
When the probe state is "10:1", the MOSI and SCK signals have the same form. 
Thank you!