PelcoD

Pelco-D is a serial communications protocol used to control PTZ (pan-tilt-zoom) CCTV cameras. Developed by Pelco (now part of Schneider Electric), it is widely supported by a range of camera manufacturers and video management systems. The protocol operates over serial links such as RS-422 or RS-485 and is designed for simple, low-bandwidth control of camera movement, zoom, focus, and presets.

A Pelco-D command is sent as a 7-byte frame. The first byte is 0xFF, used as a start delimiter. The second byte is the camera address (0x01–0xFF). The third and fourth bytes are command1 and command2, which specify the action to perform. The fifth and sixth bytes are data1 and data2, which provide parameters such as movement speed or preset values. The seventh byte is a checksum, calculated as the sum of bytes 2 through 6 modulo 256. Frames are transmitted at a fixed rate and interpreted by the addressed camera.

Typical usage involves commanding pan, tilt, and zoom actions by combining the command bytes with appropriate data values. Common actions include pan left/right, tilt up/down, and zoom in/out, as well as preset recall and set commands. A frame with zero data values generally stops movement. The address field allows control of a specific camera on a shared line; 0x00 is often reserved, while other addresses target individual units.

Pelco-D is characterized by its simplicity and broad compatibility, but it has limitations such as minimal error handling and lack of built-in acknowledgement. It remains in use in many legacy and some current CCTV deployments, frequently alongside or superseded by newer PTZ protocols.

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