Kevin Braun

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10 years, 2 months ago.  This question has been closed. Reason: Duplicate question

F746 I2C data transfer size

I ran into an issue in trying to do an I2C read of 256 bytes from a device. All data returns 0xff into the buffer and the F746 goes out to lunch, sometimes requiring the removal of power (the USB cable). I found that 255 byte I2C reads work just fine. 

//example 1
I2C i2c(I2C_SDA, I2C_SCL);
char buffer[256];

int main() {
    buffer[0] = 0;
    i2c.write(0x80, buffer, 1, true);
    i2c.read(0x81, buffer, 256, false);   //broken
    while(1) {
    //do stuff
    }
}

//example 2
I2C i2c(I2C_SDA, I2C_SCL);
char buffer[256];

int main() {
    buffer[0] = 0;
    i2c.write(0x80, buffer, 1, true);
    i2c.read(0x81, buffer, 255, false);   //works
    while(1) {
    //do stuff
    }
}

I am attempting to read the entire RTC + user RAM contents out of a DS3232M in one swoop. This code works fine on a K64F, KL25Z and nRF51822. What is the limitation on a F746?

Regards,

...kevin

Question relating to:

Last updated: 20 Apr 2021
The STM32F746G-DISCO discovery board (32F746GDISCOVERY) is a complete demonstration and development platform for STMicroelectronics ARM® Cortex®-M7 core-based STM32F746NGH6 microcontroller.

I just ran into this issue again with a 24AA02 I2C EEPROM. I am running the most current mbed library, v122. Any update?

posted by Kevin Braun 26 Jul 2016