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Cannot determine address of connected I2C device (simple I2C scanner)

Question asked by Paul Barbu on Dec 23, 2016
Latest reply on Dec 24, 2016 by Erich Styger



I have a 1602A V2.0 LCD display (16 chars x 2 lines) that I intend to connect to my  MK26 ARM M4 MCU via a LCM 1602 I2C extender (which has a Philips PCF8574AT on it).


I'm trying to get it to work since this morning, but apparently, the address I calculated for the I2C extender (0x3F according to this datasheet, A0, A1, A2 are non-jumpered) is not OK, so I tried to scan for a valid address where the I2C extender would ACK me back, but I cannot find any.

I connected just the PCF8574AT to my board, the LCD is not connected and it still doesn't work.


I have the following piece of code (KSDK 2.0):


#include "fsl_gpio.h"
#include "fsl_port.h"
#include "fsl_i2c.h"

#include "Retarget.h"
#include "Log.h"
#include <stdio.h>

#include <stdint.h>
#include <stdbool.h>

int main()

    i2c_master_config_t masterConfig;
    uint8_t status;

    /* Get default configuration for master. */
    printf("Got def. config\r\n");

    /* Init I2C master. */
    I2C_MasterInit(I2C0, &masterConfig, CLOCK_GetFreq(I2C0_CLK_SRC));


    /* Send start and slave address. */
    // 0x70, 0x27, 0x38, 0x20, 0x3F

    uint8_t u8Addr = 0x3F;

    for(u8Addr=0; u8Addr<128; u8Addr++)
        status = I2C_MasterStart(I2C0, u8Addr, kI2C_Write);

        LOG("sent address 0x%x", u8Addr);
        uint32_t u32Flags;
        /* Wait address sent out. */

        uint16_t timeout = UINT16_MAX;
        while(!((u32Flags = I2C_MasterGetStatusFlags(I2C0)) & kI2C_IntPendingFlag) && (--timeout))

        if((u32Flags = I2C_MasterGetStatusFlags(I2C0)) & kI2C_IntPendingFlag)
            LOG("ADDRESSS 0x%x IS OK", u8Addr);

        LOG("timeout is %d", timeout);

        //LOG("done address");
        status = I2C_MasterStop(I2C0);
        LOG("Stopped with status=%d", status);


Could you please point out what I'm doing wrong, why my scan doesn't yield any results?

Or is there a problem with my I2C extender, phisycally?


I'd expect the output of the above code to contain a single "ADDRESSS 0x... IS OK" line with a timeout different than 0, but that's not the case.


Merry Christmas!