VISCA control protocol

VISCA是Sony 公司設計用來控制相機的協議，一般通過RS232來通訊。以下先介紹幾個專有名詞定義

1. ACK message
   The signal from the camera to the controller returns acknowledge command execution, information for inquiry or error message, etc.
   即相機傳回的訊號。
2. Address
   The address assigned automatically by the address set command. The camera will be assigned from 1 to 7. The address of the controller is fixed to 0.
   即相機被分配 port COM 0~7。
3. Packet
   Comprised by Header (1 byte), Message (max. 14 bytes), and Terminator (1 byte; fixed FFH). Fundamental Unit of the communication between controller and cameras.
   即相機與控制器之間的通訊基本單元。
4. Socket 
   Command buffer memories prepared by camera to accept more than one commands. The number of the sockets are two.
   

Communication protocol

Communication from the controller

命令通訊的基本單元稱為包(Packet)。一個包的長度為3到16位元組(bytes)，由頭部、訊息體(message) 和結束符(terminator)三部分組成。
命令包的第一個位元組稱為命令頭，高半位元組由1 (最高位，固定為1)和傳送方(控制者)地址(地址一般為0)組成，低半位元組由0和裝置(相機)地址(或稱"編號")組成，從組成格式看，可以外接的相機最多有7臺，如向1號相機發送命令，則命令頭為0x81。
命令包最後一個位元組為終結符號，固定為0xFF。
中間部分位元組稱為訊息體，包含 communication mode (2 bytes), category code (2 bytes) and parameters. The maximum length of the message is 14 bytes.
上述命令可如下:

具體的構造如下:

Commands

從控制器發送命令大部分藏在message。命令包含了control camera (控制命令), to inquire the information (查詢命令) of the camera and the ones for various purposes.

ACK message

ACK message代表從相機回傳的訊息，包含了 camera address (expressed by z and z = address + 8), socket number (y) and terminator.
ACK completion notice, reply, or error reply from the peripheral device to the controller.

以下說明幾個常見發送gneral command 時的 REPLY ACK

• 90 41 FF (ACK) 90 51 FF  or 90 42 FF (ACK) 90 52 FF
  when a command has been accept or executed
• 90 60 02 FF 
  command syntax error
• 90 60 03 FF
  command buffer full
  
• 90 61 41 FF or 90 62 41 FF
  command not execute

以下是 inquiry command 時的 REPLY ACK

• 90 50 02 FF
  complete
• 90 60 02 FF
  command syntax error

根據以上範例，錯誤ACK可以總結如下

Error messages: