why does my OLED display with the SH1106 driver have a horizontal offset? - i2c

Question

I have a Nucleo F401RE and want to use my display with it. I have those two I2C functions:
void sh1106_sendCMD(uint8_t cmd)
{
uint8_t reg_cmd[2];
reg_cmd[0] = 0x00;
reg_cmd[1] = cmd;
HAL_I2C_Master_Transmit(&hi2c1, OLED_I2C_ADDRESS, reg_cmd, 2, HAL_MAX_DELAY);
}
void sh1106_sendData(uint8_t data)
{
uint8_t reg_data[2];
reg_data[0] = 0x40; // write data
reg_data[1] = data;
HAL_I2C_Master_Transmit(&hi2c1, OLED_I2C_ADDRESS, reg_data, 2, HAL_MAX_DELAY);
}
Then I have an init function to initialize the Display
void sh1106_init(void)
{
// Initialize the display
sh1106_sendCMD(0xAE); // Set display off
sh1106_sendCMD(0xD5); // Set display clock divide ratio/oscillator frequency
sh1106_sendCMD(0x80); // Set display clock divide ratio/oscillator frequency
sh1106_sendCMD(0xA8); // Set multiplex ratio
sh1106_sendCMD(0x3F); // 1/64 duty
sh1106_sendCMD(0xD3); // Set display offset
sh1106_sendCMD(0x00); // No offset
sh1106_sendCMD(0x40); // Set start line address
sh1106_sendCMD(0xA1); // Set segment re-map
sh1106_sendCMD(0xC8); // Set COM output scan direction
sh1106_sendCMD(0xDA); // Set COM pins hardware configuration
sh1106_sendCMD(0x12);
sh1106_sendCMD(0x81); // Set contrast control register
sh1106_sendCMD(0xFF); // Maximum contrast
sh1106_sendCMD(0xA4); // Set display to RAM
sh1106_sendCMD(0xA6); // Set normal display
sh1106_sendCMD(0xD9); // Set pre-charge period
sh1106_sendCMD(0xF1);
sh1106_sendCMD(0xDB); // Set VCOMH deselect level
sh1106_sendCMD(0x40);
sh1106_sendCMD(0x8D); // Set charge pump enable/disable
sh1106_sendCMD(0x14); // Enable charge pump
sh1106_sendCMD(0xAF); // Set display on
}
When I then try to set the pixel (x=0, y=0), nothing happens, but when I set the pixel (x=2, y=0) the pixel (x=0, y=0) turns on. Somehow I have a horizontal offset of -2.
I set the pixel like this:
sh1106_sendCMD(0xB0 | 0); // Set the page address
sh1106_sendCMD(0x02); // Set the lower column address
sh1106_sendCMD(0x10); // Set the higher column address
sh1106_sendData(0x01);

Answer 1

You probably have a 128 by 64 pixel display. The SH1106 however supports up to 132 by 64 pixel. So there are 4 unused pixel columns.
The easiest solution is to always add 2 to all x-coordinates.
If you feel more adventurous, you can configure the SH1106 accordingly. Given the limited information about your display, I can only guess. I could be:
sh1106_sendCMD(0x42);
replacing:
sh1106_sendCMD(0x40);
See the SH1106 datasheet for more information.