DDC/CI specifications

Reverse-engineered by Nicolas Boichat, using this method, go back to main DDC/CI page.

General data transfer

The DDC bus is nothing else than an I2C bus.

DDC2 informations, like monitor supported refresh rates (EDID), are transmitted using the I2C address 0x50.

DDC/CI packets are transmitted using the I2C address 0x37.

For more informations on I2C bus, see I2C specifications at Phillips.

Any application using the DDC/CI bus should make a pause of at least 30ms between every packet.

Data	Description
0x6E	I2C address : 0x37, writing
0x51	Sub-address.
0x80 OR n	Last 4 bits indicates the number of following bytes (excluding checksum)
...	n bytes
Checksum	Simple XOR of all preceding bytes (including the first)

First, send a write packet, then, when reading, the monitor returns this:

Data	Description
0x6F	I2C address : 0x37, reading
0x6E	ACK of the packet previously written.
0x80 OR n (sometimes, simply n)	Last 7 bits indicates the number of following bytes (excluding checksum)
...	n bytes
Checksum	XOR of all preceding bytes (including the first), expect the second, which is replaced by the subaddress (0x51).

First, send a 2 bytes write packet:

Data	Description
0x01	Read a value
0xXX	Index of the value to read (see below for monitor-specific indexes)

Then, read the answer (8 bytes read packet):

Data	Description
0x02	Value follows
0x00	NULL-byte
0xXX	Index of the value which is read
0x00	NULL-byte
0x00	NULL-byte
0xZZ	Maximum value (usually 0xFE)
0x00	NULL-byte
0xYY	Current value

Send a 4 bytes write packet:

Data	Description
0x03	Change a value
0xXX	Index of the value to change (see below for monitor specific indexes)
0x00	NULL-byte
0xYY	New value, in the range 0x00-0xFE

Manufacturer: MEL
Model: 4513

Index	Description	Index	Description
0x00	Degauss (value must be 0x01)	0x26	Pincushion balance
0x??	Auto-size	0x46	Top pincushion amplitude
0x??	Reset factory settings	0x48	Top pincushion balance
0x10	Brightness	0xE6	Center pincushion amplitude (value 0x00-0x01 ???, not working)
0x12	Contrast	0x4A	Bottom pincushion amplitude
0x16	Red	0x4C	Bottom pincushion balance
0x18	Green	0x3A	Vertical linearity
0x1A	Blue	0x3C	Vertical linearity balance
0x22	Width	0x28	Horizontal static convergence
0x32	Height	0x38	Vertical static convergence
0x30	Vertical position	0x56	Moire cancel
0x20	Horizontal position	0xE8	Top left screen purity
0x24	Pincushion amplitude	0xE9	Top right screen purity
0x42	Pincushion phase	0xEA	Bottom left screen purity
0x40	Keystone balance	0xEB	Bottom right screen purity

If you have other monitors, you can find these values using this method.

DDC is a trademark owned by VESA (Video Electronics Standard Association).
I2C is a trademark owned by Philips.

Please do not hesitate to contact me if you see typos, English errors or any other mistake.