Pelco-D, Pelco-PPelco-D/P are two, relatively similar communication protocols for motorized CCTV cameras.
|
The devices often feature switches for selecting the protocol within the same hardware and can be implemented in the control keypads, recorders or software, e.g. on a PC. The protocols control camera pan, focus, zoom, etc.
|
However, they are used less and less. With the high-resolution analogue systems (HD-CVI, AHD, HD-TVI), the developers have introduced new proprietary motorized camera control solutions. Pelco commands are sent with the video signal and require an extra pair of cables.
|
The signal is transmitted one-way over RS-485 at a distance of up to 1 km and the controlled device does not respond to the commands. Both systems use a 1-byte address field and allow control of up to 256 devices connected to the bus bar. The data rates are not predefined and can be selected from: 1200, 2400, 4800, 9600 bps. Wireless versions are also available.
|
The protocols support an extended command set, i.e. pre-sets - a set of commands defined by the user for automatic camera control. A motion path and speed, camera return point, fixed camera position, system reset, path function on/off can be used in automatic mode.
|
Both protocols are relatively simple. The protocol uses a 7-byte or 8-byte frame.
|
Pelco-D protocol format: Byte 1 | Byte 2 | Byte 3 | Byte 4 | Byte 5 | Byte 6 | Byte 7 | Synchronization byte | Address | Command 1 | Command 2 | Data 1 | Data 2 | Checksum |
|
Sync byte – fixed to 0xFF. Address – logical address of the camera being controlled; can control up to 256 devices. Checksum – eight bit modulo 256 checksum calculated from bytes 2 to 6. Command 1, Command 2 – command for the device; see table below for details. Data 1,Data 2 – speed of camera pan and tilt; values from 0 (stop) to 0x3F (high speed); 0xFF – turbo speed.
|
Pelco-D | Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 | Command 1 | Sense | Reserved | Reserved | Auto/manual scan | Camera on/off | Iris close | Iris open | Focus near | Command 2 | Focus far | Zoom tele | Zoom wide | Tilt down | Tilt up | Pan left | Pan right | Fixed to 0 |
|
Sense – meaning of bit 3 and 4 in command 1.
|
Pelco-P protocol format: Byte 1 | Byte 2 | Byte 3 | Byte 4 | Byte 5 | Byte 6 | Byte 7 | Byte 8 | Synchronization byte | Address | Data 1 | Data 2 | Data 3 | Data 4 | End of text | Checksum |
|
Sync byte – fixed to 0xA0. Address – logical address of the camera being controlled; control up to 256 devices. End of text – fixed to 0xAF. Checksum – xOR sum calculated from bytes 1 to 7. Data 1, Data 2 – command for the device; see table below for details. Data 3, Data 4 – speed of camera pan and tilt; from 0 (stop) to 0x3F (high speed); 0xFF – turbo speed.
|
Pelco-P | Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 | Data 1 | Fixed to 0 | Camera on | Auto scan | Camera off | Iris close | Iris open | Focus near | Focus far | Data 2 | Fixed to 0 | Zoom tele | Zoom wide | Tilt down | Tilt up | Pan left | Pan right | Pan stop |
|
|