pylon:
Show us the code and wiring you used for the 3 devices and provide links to the datasheets of the parts.There is no relevant difference between the I2C on the UNO (ATmega328) and the Mega (I guess a ATmega2560). The I2C devices I have work with both of them using the same code but of course there are differences in details because the two boards are different. The capacity of the two solutions may be slightly different, so without external pull-ups you might get different results.
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<(12864/8); 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--;
Wire.endTransmission();
}
#else
for (uint16_t i=0; i<(12864/8); 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--;
Wire.endTransmission();
}
#endif
// TWBR = twbrbackup;
}