VISCA Protocol

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VISCA is a standard developed by SONY standard for communication with video cameras. He describes both a protocol and an (optional ) network topology. VISCA devices can without addressing this, even something needs to be adjusted automatically in the device. Up to seven devices via a single serial interface (RS- 232 or RS -485) to be addressed.

Interface and wiring

VISCA can in principle with RS232, RS485 and other serial interfaces implemented. The wiring provides that the devices are connected in a circle. That is, the transmission line of the first device goes to the receive line of the second device, the second transmission line to the receiving line of the third and so on. The transmission line of the last device then goes back to the receive line of the first device. Is obtained a closed loop similar to a Token Ring network.

Under certain circumstances, the data packets must pass all instruments. Only the addressed device uses the data packet destined for itself and then sends reception and execution confirmations on, which are sent back to the sender at the end of the chain.

The sender can then see, for example, if a command in the chain has remained unfinished when he gets back the package again.

The default communication parameters for RS232 or RS485 communication with VISCA are 9600 baud, 8 data bits, 1 start bit, 1 stop bit, no parity. Some cameras can also be addressed with higher baud rates. Recognition is usually automatically.

Protocol

The VISCA protocol is relatively simple. It always consists of 3 to a maximum of 16 bytes. The first and last bytes have a fixed meaning. The remaining bytes are free. The last byte is always the end character FFh. It may not otherwise occur within the VISCA package!

VISCA packages can be divided into commands and responses. Commands are sent from the controller (eg PC or controller) to the cameras. Answers are the confirmation messages from the cameras.

VISCA commands always begin with the address of the addressed device ( 81h to 87h ). If the address is 88h, so all devices are addressed. 88h is the so-called " broadcast address ".

VISCA answers always begin with the return address of the responding device ( 90h to F0h ). The reply address is different than the address of the addressed device in command. This can be seen directly, whether it is a command or a response. So, for example, has the first device in the chain, the address 81h and his reply address is 90h. The second device has the address 82h and his reply address is A0h. The third device has an address of 83h and his reply address is B0h and so on.

Example:

The controller asks the first camera on the current zoom value. He sends the command 81 09 04 47 FF ( hex). The camera responds to example 90 50 00 00 00 00 FF ( hex). The 90h is the reply address of the camera with the address 81h.

Addressing

Addressing is performed at VISCA automatically. The address assignment is in the order of wiring the device. The controller sends the packet 88 30 01 FF ( hex). The first device in the chain analyzes the packet and gets the address 81h assigned, which is derived from the third byte in the packet ( 01h). It is incremented by one byte ( 02h) and sends the packet, which then is further FF 88 30 02 to the second camera. The second unit in the chain will get the address of allocated 82h and so on. The last device in the chain sends the packet thus generated back to the controller. This can be seen from the response of the chain, how much cameras are in the chain. Are allowed up to seven cameras.

Differences for Pelco -D / P protocol

The main difference from the Pelco -D / P protocol is the lack of a checksum at VISCA and the type of addressing. Some Pelco -D / P is the address in the device is fixed or programmed ( via DIP switch or the like) in VISCA it is, however, dynamically allocated, and results from the order in the wiring. Therefore, in VISCA is a larger effort in the wiring to make. VISCA is also more sensitive to line breaks (affects the entire chain ) during Pelco -D / P through the star-shaped structure which is compared with more robust.

Therefore VISCA is suitable for use on short distances and probably not for a larger area.

Pelco -D / P allows the addressing of up to 256 different cameras during VISCA knows only up to seven addresses.

There are also protocol converter Pelco -D / P on VISCA to bring together both systems and to combine the advantages and disadvantages.

Dissemination

VISCA is in almost all camera blocks from Sony such as FCB - EX480, FCB - EX780 etc available. This camera blocks are mainly used in the field of security and other manufacturers are also integrated into products. There are also cameras with integrated pan-tilt - head of SONY, such as EVI- D31 or EVI -D100. Since these cameras are not suitable for use outdoors or in the industrial environment, there are also control devices for robust weatherproof pan-tilt heads that support the VISCA protocol and SONY cameras like DCP -30 or DCP -18 GNT.