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STM32F429I-DISCO and XTAL X3 8MHz

Question asked by ricardo on Oct 21, 2014
Latest reply on Oct 24, 2014 by Clive One
Hi,

Its my first time here!

I have a STM32F429I-DISCO, original from factory.

I used the STM32CubeMX with STM32Cube_FW_F4_V1.3.0 to build a code.
I selected "new project\board selector\Type of Board: Discovery\Series: STM32F4\Board List: STM32F429iDISCOVERY"
In the Clock Configurations, all items seemed OK.
If I properly understood the manual, the HSE is used for external xtal.
In this kit, this crystal is the X3... A 8MHz xtal.
I put a screenshot of STM32CubeMX Clock Configurations here.

I built a very simple code to the first test of my kit.

01./* USER CODE BEGIN 3 */
02.BSP_LED_Init(LED3);
03. 
04./* Infinite loop */
05.while (1)
06.{
07. __asm(
08.      "ldr r1, =0x40021800;"
09.      "ldr r3, [r1,#20];"
10. "loop:;"   
11.      "eors r3, 0x2000;" 
12.      "str r3, [r1,#20];"
13.      "b loop;"
14.     );
15.}
16./* USER CODE END 3 */

This code will switch the output port PG13, referring to LED3.
I could see a waveform with these following time base:
       ____      _...
  ..._|    |____|
      +---50nS--+

Until this point everything seemed OK.

However, when I pulled the X3 crystal, to my surprise, the kit remained operational!!!
I can not understand how this is possible!!!
Would you could help me with this?

Now, I'm not even sure if the kit is running at the correct frequency of 180MHz!!!

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