DDC/CI詳解 - I

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DDC/CI（Display Data Channel / Command Interface）是一種顯示器和電腦之間的通訊協議，

用來讓電腦直接控制顯示器的設定，而不需要手動操作螢幕上的按鈕。


實體接口

HDMI透過 第15 pin(SCL), 16 pin(SDA), 17 pin(Gnd) 以I2C來溝通


DP (DisplayPort)則是以 AUX_CH(P)及AUX_CH(N)來通訊

DDC/CI Host Device

DDC/CI主機是I2C的master，I2C slave address為0x50 / 0x51


DDC/CI Display Device

DDC/CI顯示裝置的I2C slave address為0x6E / 0x6F


DDC/CI Communication Basic Commands

Get VCP Feature 0x01 告知要讀取 VCP opcode
VCP Feature Reply 0x02 讀取 VCP 功能 最大值 / 目前值
Set VCP Feature 0x03 設定VCP功能值
Reply Timing Message 0x06 取得目前輸入影像時序（H/V freq、pixel clock）
Get Timing Report 0x07 告知要讀取影像時序
Save Current Setting 0x0C 儲存目前設定值
Capabilities Request Reply 0xE3 回傳 Capabilities String
Capabilities Request 0xF3 要求顯示器回傳能力字串

Get VCP Feature & VCP Feature Reply

要讀取VCP code的內容必須先用Get VCP Feature 0x01告知裝置VCP code

然後再用VCP Feature Reply 0x02取值

VCP：Virtual Control Panel（虛擬控制面板）


Get VCP Feature

6E 51 82 01 CP CK

Destination address

Source address

Length

Get VCP Feature

VCP opcode

Checksum

  • 6E：顯示裝置的I2C address
  • 51：source的address
  • 82：data的長度2個bytes，不包含checksum，bit 7固定為1
  • 01：command "Get VCP Feature"
  • CP：VCP code
  • CK：checksum，所有位元做XOR

VCP Feature Reply

6F (read 11 bytes)

6E 88 02 RC CP TP MH ML SH SL CK

Destination address

Source address

Length

VCP Feature reply

Result Code

00h: No Error

01h: Unsupported VCP Code

VCP opcode

VCP type code

00h: Set parameter

01h: Momentary

Maximum value High byte

Maximum value Low byte

Present value High byte

Present value Low byte

Checksum

  • 6F：顯示裝置的I2C read address
  • (byte 0) 6E：顯示裝置的I2C address
  • (byte 1) 88：Length | 0x80，data的長度8個bytes，不包含checksum
  • (byte 2) 02：command "VCP Feature Reply"
  • (byte 3) RC：Result code。00h:成功，01h:不支援的VCP code，02h:VCP code無效，03h:操作失敗
  • (byte 4) CP：VCP code
  • (byte 5) TP：資料的型態。00h:可設定參數，01h:觸發型
  • (byte 6) MH：可設定最大值的高位元
  • (byte 7) ML：可設定最大值的低位元
  • (byte 8) SH：目前數值的高位元
  • (byte 9) SL：目前數值的低位元
  • (byte 10) SL：checksum

> I2C Write, Address = 6E, Data: 51 82 01 10 AC Delay = 0
OK
> I2C Read, Address = 6F, Read 11 bytes, Delay = 0
OK
< 6E 88 02 00 10 00 00 64 00 32 F2

讀取VCP code 0x10 (Luminance)亮度

最大值0x0064 (100)，目前值為0x0032 (50)


Set VCP Feature

用於寫入某個 VCP Code 的值，相當於“設置顯示器參數”。


Set VCP Feature

6E 51 84 03 CP SH SL CK

Destination address

Source address

Length

Get VCP Feature

VCP opcode

High byte

Low byte

Checksum

  • 6E：顯示裝置的I2C address
  • 51：source的address
  • 84：data的長度4個bytes，不包含checksum，bit 7固定為1
  • 03：command "Set VCP Feature"
  • CP：VCP code
  • SH：輸入值的高位元
  • SL：輸入值的低位元
  • CK：checksum，所有位元做XOR

> I2C Write, Address = 6E, Data: 51 84 03 10 00 64 CC Delay = 0
OK

設定VCP code 0x10 (Luminance)亮度為100%


Get Timing Report & Reply Timing Message

用來取後影像訊號的H/V頻率

要讀取VCP code的內容必須先用Get Timing Report 0x07通知裝置VCP code

然後再用Reply Timing Message 0x06取值


Get Timing Report

6E 51 81 07 B9

Destination address

Source address

Length

Get Timing Report

Checksum


Reply Timing Message

6F (read 9 bytes)

6E 06 4E SS HH HL VH VL CK

Destination address

Source address

Reply Timing Message

Timing message op code

Timing Status byte

Bit 7 = 1 Sync.Freq. out of range

Bit 6 = 1 Unstable count

Bit 5-2 Reserved, shall be set to 0

Bit 1 = 1 Positive Horizontal sync polarity

Bit 1 = 0 Negative Horizontal sync polarity

Bit 0 = 1 Positive Vertical sync polarity

Bit 0 = 0 Negative Vertical sync polarity

Horizontal Frequency High byte

Horizontal Frequency Low byte

Vertical Frequency High byte

Vertical Frequency Low byte

Checksum

  • 6E：顯示裝置的I2C address
  • 06：Reply Timing Message
  • 4E：Timing message op code
  • SS：Timing Status byte
  • HH：Horizontal Frequency High byte
  • HL：Horizontal Frequency Low byte
  • VH：Vertical Frequency High byte
  • VL：Vertical Frequency Low byte
  • CK：checksum，所有位元做XOR

> I2C Write, Address = 6E, Data: 51 81 07 B9 Delay = 0
OK
> I2C Read, Address = 6F, Read 9 bytes, Delay = 0
OK
< 6E 06 4E 02 34 1C 17 70 3B

Horizontal頻率為0x341C (13340 = 133.4MHz)

Vertical頻率為0x1770 (6000 = 60.0Hz)


Save Current Setting

儲存目前設定值


Save Current Setting

6E 51 81 0C B2

Destination address

Source address

Length

Save current settings

Checksum


Capabilities Request & Capabilities Request Reply

apabilities Request 用于獲取顯示器的 Capabilities String，也叫能力描述字符串。


Capabilities Request

6E 51 83 F3 OH OL CK

Destination address

Source address

Length

Capabilities Request

Offset value High byte

Offset value Low byte

Checksum


Capabilities Reply

6F (read 9 bytes)

6E XX E3 OH OL Data(n) CK

Destination address

Source address

Length (length=3~35)

Capabilities reply op code

Offset High byte

Offset Low byte

Capability string data

Checksum

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