I2C is different between MEGA and UNO?

Other Hardware 3rd Party Boards
1

I have been experience some I2C problems between MEGA and UNO. First I wire a I2C device#1 to MEGA, and works fine. Then I wire the device#1 to UNO and the same program, and it doesn't work.

A few days later, I did another experiment. I wire I2C device#2?which works with UNO each time) to MEGA, and it doesn't work with the same program.

Then I did a final test with I2C device#3, I work with MEGA at both 400kbps and 100kbps rate, but device#3 can only works with UNO at 100kbps rate.

Can anyone tell me the reason?

2

What program? What wiring? More details.

3

One of the device is http://www.geekonfire.com/wiki/index.php?title=I2C_OLED_Panel(128x64)#Resources. It works on UNO and MEGA at 100kbps, but at 400kbps only works at MEGA.(I have tested it on MEGA2560,MEGA1280 and MEGA Olympic)

code in library:
//uint8_t twbrbackup = TWBR;
//TWBR = 12; // upgrade to 400KHz!
// TWBR = twbrbackup;
if I enable the above sentences, It doesn't work at UNO.

void GOFi2cOLED::display(void) {
  sendCommand(0x00 | 0x0);  // low col = 0
  sendCommand(0x10 | 0x0);  // hi col = 0
  sendCommand(0x40 | 0x0); // line #0

    // save I2C bitrate
    //uint8_t twbrbackup = TWBR;
    //TWBR = 12; // upgrade to 400KHz!

    // I2C
    #if defined(ARDUINO) && ARDUINO >= 100
    for (uint16_t i=0; i<(128*64/8); i++) 
    {
      // send a bunch of data in one xmission
      Wire.beginTransmission(SlaveAddress);
      Wire.write(GOFi2cOLED_Data_Mode);            // data mode
      for (uint8_t x=0; x<16; x++) 
      {
        Wire.write(buffer[i]);
        i++;
      }
      i--;
      Wire.endTransmission();
    }      
    #else
    for (uint16_t i=0; i<(128*64/8); i++) 
    {
      // send a bunch of data in one xmission
      Wire.beginTransmission(SlaveAddress);
      Wire.send(GOFi2cOLED_Data_Mode);            // data mode
      for (uint8_t x=0; x<16; x++) 
      {
        Wire.send(buffer[i]);
        i++;
      }  
      i--;
      Wire.endTransmission();
    }
    #endif    
//    TWBR = twbrbackup;
}
4

There is confusion when you say "enable all above sentences". Please post the specific code which works on the atmega2560 but not the Uno. (code that I can copy and paste into an IDE, without having to physically take out specific comments you have).

5

Please edit your post, select the code, and put it between [code] ... [/code] tags.

You can do that by hitting the # button above the posting area.

6

Have anyone had any idea?