Hugo Arriaga

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8 years, 8 months ago.

ports working at 6 MHz i want to operate the ports at 84 MHz

hi, i am working with F401re, only that the all ports working to 6 MHz, how do i operate the F401RE ports a 84 MHZ?, i put this instruction pc.printf("CPU SystemCoreClock is %d Hz\r\n", SystemCoreClock); and the results is CPU SystemCoreClock is 84000000 Hz but the ports do not operate at 84 MHz, they operate a 6 MHz

please you help me await for your answer asap best regards

Question relating to:

Last updated: 08 Apr 2014
Lib to switch the clock speed of the ST Nucleo to 84MHz. The internal RC oscillator is multiplied with the PLL. clock, f401, Nucleo

Thanks you for helping me, I must to read 16 signals at 6 MHz, at the same time , do you think that with the F401RE i can read 16 signals at 6 MHz? how many time last one instruction at F401RE? how many clock cycles is a instruction at F401RE?

What do you want to do with the 5 megapixels? anwers: Compare all the pixels until find the pixel with higher voltage, I wish not to save the value of these pixels, only compare

excuse for many questios only have little weeks use the F401RE

thanks for helping me

posted by Hugo Arriaga 10 Sep 2015

Peter, you says below?

He check CPU Speed is 84MHz. CPU must read ports 16ports by software loop 6MHz clock.

He want to know How do I take more sampling speed in his software loop? So he says : How do I know cpu instruction cycles with mbed?

posted by p igmon 14 Sep 2015

1 Answer

Erik -
8 years, 8 months ago.

It takes multiple clock cycles to toggle a port pin. This is on every MCU, and normally you also want to do some calculations in between. If you just want to toggle an output all the time, use a PWM output.

FastIO will be a bit faster, but the regular lib is quite efficient for the F401 at toggling an output (don't try to toggle between input and output however, thats horribly slow with the standard lib, and FastIO is alot more efficient for that).

Accepted Answer

Excuse me, it is possible that you give me examples about this, and how many clock cycles is a instrucción? Besause for my proyect is very importante the time of a instruction So sorry i have a some weeks to drive this F401RE microcontroler

Thanks very muchos fpr help me Best regards

posted by Hugo Arriaga 09 Sep 2015

For FastIO and comments regarding GPIO speed, see: https://developer.mbed.org/users/Sissors/code/FastIO/. But if your describe your requirements we might be able to help you better.

posted by Erik - 09 Sep 2015

thank you for helping me, i am working with image CMOS active pixel, this image cmos active pixel work a minimum frecuency of 6 MHz , and the image CMOS active pixel have 5 Mega pixels,i work with this microcontroller F401RE because the datasheet mark that it is working a maximum frecuency of 84 MHz, I must need the F401RE work minimum 24 MHz by instruction because I can work and read the image CMOS active pixel, how the does F401RE work minimum 24 MHz by instruction? I must need to read some signal with F401RE from image CMOS active pixel a frecuency of 6 MHz.

thank you helping me await for your comments and answers best regards

Hugo A

posted by Hugo Arriaga 10 Sep 2015

What do you want to do with the 5 megapixels? The F401 hasn't nearly enough memory to store that amount of data.

Generating a 24MHz clock is easy, reading the data is harder. If it is a single wire, use SPI to read. Otherwise DMA can help, but in general I doubt you ever reach the speed you want it to work at.

posted by Erik - 10 Sep 2015