Software I2C - ATmega8

Question

I am using ATmega8 with 12MHz crystal, on my breadboard. I can use SDA and SCL pins with default arduino library wire.h, and it works. But I want another pins to use I²C protocol.

I tried this library, even on real SDA and SCL pins, but it doesn't work.

I have pull up resistors, I tried with 10k and 4.7k without any success. (But those resistors worked with hardware I²C | TWI)

What am I doing wrong? (All connections is fine, because hardware TWI works but software does not.) Thank you for your help.

(Fuses are ok, because the Atmega won't respond if I remove the crystal oscillator, the LED blinking duration is ok.)

What i want to run (that doesn't work):

#define SDA_PORT PORTC
#define SDA_PIN 4
#define SCL_PORT PORTC
#define SCL_PIN 5
//#define I2C_TIMEOUT 100
#include <SoftI2CMaster.h>
uint8_t ADDR = 0x68;
void setup(void) {
 Serial.begin(19200);
 Serial.println("Initializing ...");
 i2c_init();
 if (!i2c_start(ADDR | I2C_WRITE)) Serial.println(F("Device does not respond"));
 if (!i2c_write(0x00)) Serial.println(F("Cannot address reg 0"));
 i2c_stop();
} 
void loop (void) {
 unsigned int low0, high0, low1, high1;
 unsigned int chan0, chan1;
 unsigned int lux;
 int state1;
 int state2;
 delay(1000);
 i2c_start(ADDR | I2C_WRITE);
 i2c_write(0x00);
 i2c_rep_start(ADDR | I2C_READ);
 low0 = i2c_read(false);
 high0 = i2c_read(false);
 low1 = i2c_read(false);
 high1 = i2c_read(true);
 i2c_stop();
 Serial.print(low0);
}

And the code with hardware TWI that works:

#include "Wire.h"
#define DS3231_I2C_ADDRESS 0x68
// Convert normal decimal numbers to binary coded decimal
byte decToBcd(byte val)
{
 return( (val/10*16) + (val%10) );
}
// Convert binary coded decimal to normal decimal numbers
byte bcdToDec(byte val)
{
 return( (val/16*10) + (val%16) );
}
void setup()
{
 Wire.begin();
 Serial.begin(19200);
 pinMode(13, OUTPUT);
 pinMode(5, INPUT);
}
void readDS3231time(byte *second,
byte *minute,
byte *hour,
byte *dayOfWeek,
byte *dayOfMonth,
byte *month,
byte *year)
{
 Wire.beginTransmission(DS3231_I2C_ADDRESS);
 Wire.write(0); // set DS3231 register pointer to 00h
 Wire.endTransmission();
 Wire.requestFrom(DS3231_I2C_ADDRESS, 7);
 // request seven bytes of data from DS3231 starting from register 00h
 *second = bcdToDec(Wire.read() & 0x7f);
 *minute = bcdToDec(Wire.read());
 *hour = bcdToDec(Wire.read() & 0x3f);
 *dayOfWeek = bcdToDec(Wire.read());
 *dayOfMonth = bcdToDec(Wire.read());
 *month = bcdToDec(Wire.read());
 *year = bcdToDec(Wire.read());
}

Schematic is the same as: https://www.arduino.cc/en/main/standalone.

Except instead of 16MHz, I use a 12MHz and ch210x serial.

Arduino's bootloader works well, I compiled it from source.

• Ricardo: It would help if you posted code and schematics of both situations (hardware and software I2C attempts). Also, to debug I2C effectively, you'd need a logic analyzer or at very least an oscilloscope.
• Gerben: What do you get on the serial output?
• ONSC: Initializing ... Device does not respond Cannot address reg 0 SDA - SCL 0 0 Raw values: chan0=65535 SDA - SCL 0 0
• ONSC: actually i should get the ohur:minute:second day/month/year that i can get in hardware twi,
• ONSC: i ve removed some of code, just before he stop function , i get the pinstate to whats happening, so that output is showed

Answer 1

OK let me cry till morning...

i was having this issue during day, but the solution was sooo easy

i need to pay attention more ...

i2c_start(addr | R/W-bit) Initiates a transfer to the slave device with the (8-bit) I2C address addr.

what i was trying is to push 7 bit address.

i hope this might help some others.

Thank you for help.