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PIC32MK1024MCM064 I2C setup problem

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Newbie level 4
Jul 24, 2022
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Hi guys,
I have been learning to program mentioned PIC32 model for quite some time for a big project in the future. I came to I2C communication part which will be key feature in my project, I have not done anything with an I2C protocol in the past on any microcontroller ever, so I am a complete beginner with I2C. For now, my program goal is to write anything to 24LC512 eeprom chip via I2C bus (since I am working on a breadboard, the verification that eeprom was written successfully would be reading the eeprom with my TL866II+ memory programmer and seeing the data I wrote to eeprom via my pic32 code). After examining protocol`s architecture and hours of datasheet reading I came up with some I2C setup code (I know it may not be very efficient, but lets not take it so far right now). And that code seems partially correct. I looked at my SDA and SCL lines via logic analyzer and I saw some casual I2C data packet (using 100kbit/s so 50kHz frequency). However, when I hooked my 24LC512 to the TL866II+ and read it, the memory map was completely empty (TL866II+ is working properly, I verified it in the past). So where is the problem? My 24LC512 wiring:

Vdd is at +3.3V
A2 A1 A0 all grounded
WP is directly connected to Vdd (to enable write operations to the chip)
SDA and SCL both pulled up via 5.1k ohm resistors

I am not sure is it even a software problem, but my wiring looks just like the 24LC512 datasheet recommendations, and I am getting an actual I2C data packet on my SDA line at 100 kbit/s or 50 kHz (as you like it). This looks quite scary to me, because I have no idea what to look for anymore. I really appreciate any help or hints for the beginner of fabulous I2C world.


// PIC32MK1024MCM064
#pragma config USERID = 0xFFFF          // Enter Hexadecimal value (Enter Hexadecimal value)
#pragma config PWMLOCK = OFF            // PWM IOxCON lock (PWM IOxCON register writes accesses are not locked or protected)
#pragma config FUSBIDIO2 = ON           // USB2 USBID Selection (USBID pin is controlled by the USB2 module)
#pragma config FVBUSIO2 = ON            // USB2 VBUSON Selection bit (VBUSON pin is controlled by the USB2 module)
#pragma config PGL1WAY = OFF            // Permission Group Lock One Way Configuration bit (Allow multiple reconfigurations)
#pragma config PMDL1WAY = OFF           // Peripheral Module Disable Configuration (Allow multiple reconfigurations)
#pragma config IOL1WAY = OFF            // Peripheral Pin Select Configuration (Allow multiple reconfigurations)
#pragma config FUSBIDIO1 = ON           // USB1 USBID Selection (USBID pin is controlled by the USB1 module)
#pragma config FVBUSIO1 = ON            // USB2 VBUSON Selection bit (VBUSON pin is controlled by the USB1 module)
#pragma config FPLLIDIV = DIV_1         // System PLL Input Divider (1x Divider)
#pragma config FPLLRNG = RANGE_BYPASS   // System PLL Input Range (Bypass)
#pragma config FPLLICLK = PLL_FRC     // System PLL Input Clock Selection (FRC is input to the System PLL)
#pragma config FPLLMULT = MUL_2         // System PLL Multiplier (PLL Multiply by 1)
#pragma config FPLLODIV = DIV_2        // System PLL Output Clock Divider (2x Divider)
#pragma config BORSEL = HIGH            // Brown-out trip voltage (BOR trip voltage 2.1v (Non-OPAMP deviced operation))
#pragma config UPLLEN = OFF             // USB PLL Enable (USB PLL Disabled)
#pragma config FNOSC = FRC              // Oscillator Selection Bits (Internal Fast RC (FRC))
#pragma config DMTINTV = WIN_0          // DMT Count Window Interval (Window/Interval value is zero)
#pragma config FSOSCEN = OFF            // Secondary Oscillator Enable (Disable Secondary Oscillator)
#pragma config IESO = OFF               // Internal/External Switch Over (Disabled)
#pragma config POSCMOD = OFF            // Primary Oscillator Configuration (Primary osc disabled)
#pragma config OSCIOFNC = OFF           // CLKO Output Signal Active on the OSCO Pin (Disabled)
#pragma config FCKSM = CSDCMD           // Clock Switching and Monitor Selection (Clock Switch Disabled, FSCM Disabled)
#pragma config WDTPS = PS1              // Watchdog Timer Postscaler (1:1)
#pragma config WDTSPGM = STOP           // Watchdog Timer Stop During Flash Programming (WDT stops during Flash programming)
#pragma config WINDIS = NORMAL          // Watchdog Timer Window Mode (Watchdog Timer is in non-Window mode)
#pragma config FWDTEN = OFF             // Watchdog Timer Enable (WDT Disabled)
#pragma config FWDTWINSZ = WINSZ_25     // Watchdog Timer Window Size (Window size is 25%)
#pragma config DMTCNT = DMT31           // Deadman Timer Count Selection (2^31 (2147483648))
#pragma config FDMTEN = OFF             // Deadman Timer Enable (Deadman Timer is disabled)
#pragma config DEBUG = OFF              // Background Debugger Enable (Debugger is disabled)
#pragma config JTAGEN = OFF             // JTAG Enable (JTAG Disabled)
#pragma config ICESEL = ICS_PGx3        // ICE/ICD Comm Channel Select (Communicate on PGEC3/PGED3)
#pragma config TRCEN = OFF              // Trace Enable (Trace features in the CPU are disabled)
#pragma config BOOTISA = MIPS32         // Boot ISA Selection (Boot code and Exception code is MIPS32)
#pragma config FECCCON = ECC_DECC_DISABLE_ECCON_WRITABLE// Dynamic Flash ECC Configuration Bits (ECC and Dynamic ECC are disabled (ECCCON<1:0> bits are writable))
#pragma config FSLEEP = OFF             // Flash Sleep Mode (Flash is powered down when the device is in Sleep mode)
#pragma config DBGPER = PG_ALL          // Debug Mode CPU Access Permission (Allow CPU access to all permission regions)
#pragma config SMCLR = MCLR_NORM        // Soft Master Clear Enable (MCLR pin generates a normal system Reset)
#pragma config SOSCGAIN = G3            // Secondary Oscillator Gain Control bits (Gain is G3)
#pragma config SOSCBOOST = ON           // Secondary Oscillator Boost Kick Start Enable bit (Boost the kick start of the oscillator)
#pragma config POSCGAIN = G3            // Primary Oscillator Coarse Gain Control bits (Gain Level 3 (highest))
#pragma config POSCBOOST = ON           // Primary Oscillator Boost Kick Start Enable bit (Boost the kick start of the oscillator)
#pragma config POSCFGAIN = G3           // Primary Oscillator Fine Gain Control bits (Gain is G3)
#pragma config POSCAGCDLY = AGCRNG_x_25ms// AGC Gain Search Step Settling Time Control (Settling time = 25ms x AGCRNG)
#pragma config POSCAGCRNG = ONE_X       // AGC Lock Range bit (Range 1x)
#pragma config POSCAGC = Automatic      // Primary Oscillator Gain Control bit (Automatic Gain Control for Oscillator)
#pragma config EJTAGBEN = NORMAL        // EJTAG Boot Enable (Normal EJTAG functionality)
#pragma config CP = OFF                 // Code Protect (Protection Disabled)
// SEQ
#pragma config TSEQ = 0x0               // Boot Flash True Sequence Number (Enter Hexadecimal value)
#pragma config CSEQ = 0xFFFF            // Boot Flash Complement Sequence Number (Enter Hexadecimal value)
#include <xc.h>                        
#include <toolchain_specifics.h>      
#include <stddef.h>                  
#include <stdint.h>                  
#include <stdbool.h>                  
#include <stdlib.h>
#include "stdio.h"
#include <sys/attribs.h>                      
#define CPU_CLOCK_FREQUENCY 8000000
#define _CP0_GET_COUNT()  _mfc0 (_CP0_COUNT, _CP0_COUNT_SELECT)
#define MASTER_WRITE_24LC512_ADDRESS (0B10100000)     //Last bit is R/W (1 for reading, and 0 for writing)
#define MASTER_READ_24LC512_ADDRESS (0B10100001)      //Last bit is R/W (1 for reading, and 0 for writing)
void delay_ms ( uint32_t delay_ms)
    uint32_t startCount, endCount;


void I2C__initialization(void){
    //The datasheet declares that when the I2C module is enabled pins are assigned automatically
    //(For I2C module nr.1 SCL is pin 5 and SDA is pin 6 ) and TRIS bits are overriden anyway.
    //I believe there is nothing else to do with I2C pin setup other than enabling the I2C module
    //PIC is operating in master mode, so address and address mask register are irrelevant for this application.
    //PB2CLK is same as SYSCLK here (8Mhz)
    ANSELG = 0xFFFFFE7F;          //Enable digital inputs for I2C pins (Clear ANSEL RG7 and RG8)      
    I2C1BRG = 0x00000010;         //Baud rate setup register (Here 50 kHz for the 100kb/s data rate)
    I2C1CON = 0x00000000;         //Resetting register to clear all bits (to ensure right setup)
    I2C1CONbits.SDAHT = 0b1;      //Minimum of 300 ns hold time on SDA after the falling edge of SCL
    I2C1CONbits.SIDL = 0b1;       //Discontinue module operation when device enters Idle mode
    I2C1CONbits.SCLREL = 0b1;     //Release SCL clock
    I2C1CONbits.DISSLW = 0b1;     //Slew rate control is disabled
    I2C1CONbits.SMEN = 0b0;       //Disable SMBus input thresholds
    I2C1CONbits.ON = 0b1;         //Enable I2C module
void I2C__state(void){
    while( (I2C1CON & 0x0000001F) || (I2C1STAT & 0x00000004) );  //Checking is the I2C bus is idle, waiting until it becomes idle (checking all I2C status bits)
void I2C__Start(void){
    I2C1CONbits.SEN = 0b1;     //Initiate Start condition on SDAx and SCLx pins
void I2C__Stop(void){
    I2C1CONbits.PEN = 0b1;    //Initiate Stop condition on SDAx and SCLx pins
void I2C_Repeated_Start(void){
    I2C1CONbits.RSEN = 0b1;   //Initiate Repeated Start condition on SDAx and SCLx pins
void I2C__Write(uint8_t I2C_data){
    while(I2C1STATbits.TBF != 0);        //Ensuring the transmit buffer is completely empty before the new transmission
    while(I2C1STATbits.TRSTAT != 0);     //Ensuring the transmission has ended
    I2C1TRN = I2C_data;                  //Loading the data to the I2C transmit buffer for transmission
uint8_t I2C__Read (uint8_t ACK){
   uint8_t data = 0;
   I2C1CONbits.RCEN = 0b1;            //Enables Receive mode for I2C
   while(I2C1STATbits.RBF != 0);      //Ensuring the receive buffer is completely empty before new reception
   data = (I2C1RCV & 0x000000FF);     //Extracting lower 8 bits of the I2C data from a 32 bit I2C receive register
   I2C1CONbits.ACKEN = ACK;
   return data;
int main ( void )
    TRISCbits.TRISC0 = 1;    //Button input setup
    ANSELC = 0x00000000;     //Enable PORT C digital inputs (VERY IMPORTANT)
    TRISAbits.TRISA7 = 0;
    LATAbits.LATA7 = 0;      //LED 1
    TRISBbits.TRISB14 = 0;
    LATBbits.LATB14 = 0;     //LED 2
    TRISBbits.TRISB15 = 0;
    LATBbits.LATB15 = 0;     //LED 3
    TRISGbits.TRISG6 = 0;
    LATGbits.LATG6 = 0;      //LED 4
    TRISGbits.TRISG9 = 0;
    LATGbits.LATG9 = 0;      //LED 5
    TRISAbits.TRISA12 = 0;
    LATAbits.LATA12 = 0;     //LED 6
    TRISAbits.TRISA11 = 0;
    LATAbits.LATA11 = 0;     //LED 7
    while (1)
        //Background blinking leds
        LATBbits.LATB14 = 1;
        LATBbits.LATB14 = 0;
        LATBbits.LATB15 = 1;
        LATBbits.LATB15 = 0;
        if(!PORTCbits.RC0){    //Button pressed condition
            LATAbits.LATA7 = 1;
            I2C__Write(0x00);                          //EEPROM`s address higher 8 bits (random number for testing)
            I2C__Write(0x11);                          //EEPROM`s address lower 8 bits (random number for testing)
            I2C__Write(0x49);                          //Writing random number to the EEPROM memory cell
            LATAbits.LATA7 = 0;
    return (EXIT_FAILURE);


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Last edited by a moderator:

Yes you were right, I should have tied WP to ground, but even after doing that, I get exactly same result... I can not understand it.... Not to mention that I double checked TL866II+. When I write something to eeprom via TL866II+ and then read it, I can see exactly same data I written, so TL866II+ is really working as it should be... Maybe my addressing is bad or something else? I dont know much about SMbus, should I enable itor disable it? Is there any difference on 100 and 300 ns hold time on SDA after the falling edge of SCL. Is there any other setup secrets of the I2C?
Last edited:

A couple of suggestions that are not related to your problem directly.
Firstly, don't specify anything for the DEBUG config value - leave that to the IDE to set for you as there are more differences between debug and release builds than just setting this item.
Secondly, there are a number of I2C code examples out there. Also try using the MCC to give you some ideas for your code. I think MCC generates garbage code (as in way too over-complicated) but it does (eventually) work.

About the MCC thing. I really had some unpleasant experience with it, when I just started learning this pic I did a PWM code setup which was not working with MCC code, only after a few of my own adjustments I got it working. Also MCC generates really complicated code with various classes and structures which really takes a lot of MCU memory and is really hard to analyze it well. However, since I am getting the standard I2C data packet, do you really suggest my overwriting my code all from zero again? I guess it is a single parameter bug somewhere, but I can not think of any.... And then there is the hardware, but like I mentioned, I don`t know what to change in it anymore...

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