Pelco P and D protocol implementation in C#

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Introduction

This is GPL software. Do with it as you want, but feed us back any improvements.

This is a full C# classes to control a PELCO PTZ cameras, matrix switching systems,
reciever devices and more via RS422/485 'P' and 'D' protocol.
It supports all of the commands including UP, DOWN, IN, OUT, LEFT, RIGHT, NEAR, FAR, as well as other extended commands.

To use this, you need to put a RS232->RS422 adapter on the output of your desired serial port.

The Pelco doesn't return ANY usefull info back, so you only really need 2-wire support (one way) communications out. However, I advice to read it in order to know if the command was recieved by the device.

This section describes the protocol used when sending commands to an Intercept Dome in the �P� version protocol and Coaxitron series equipment and with Pelco�s �D� version receivers. Those protocols use no parity, one start bit, eight data bits, and one stop bit. The recommended baud rate is 4800 (4800, 8, N, 1, 1).

Theory

In those protocols the messages structure are different. However both of protocols using RS-485 port to send and recieve messages.

All values below are shown in hexadecimal (base 16).

Pelco P message structure

Byte 1 is always $A0
Byte 2 is the receiver address, set by DIP switch in the receiver
Byte 3-6, see below
Byte 7 is always $AF
Byte 8 is an XOR sum of Bytes 1-7

The protocol is �zero indexed� so that the hexadecimal address sent in the protocol for the first receiver is $00 which corresponds to address 1.

Pelco D message structure

The �D� protocol has some added overhead to improve the reliability of transmissions. The format for a message is:

The synchronization byte is always $FF.

The address is the logical address of the receiver/driver being controlled.

Following structs that bulds those message and prepare them to be sent to the device

public struct Message // Pelco P Message

  {
   public static byte Address;
   public static byte CheckSum;
   public static byte Data1,Data2,Data3,Data4;

 

   public static byte[] GetMessage(uint address, byte data1, byte data2, byte data3, byte data4)
   {
    if (address<0 & address>32)
     throw new Exception("Protocol Pelco P support 32 devices only");

 

    Address = Byte.Parse((address-1).ToString());
    Data1 = data1;
    Data2 = data2;
    Data3 = data3;
    Data4 = data4;

 

    CheckSum = (byte)(STX ^ Address ^ Data1 ^ Data2 ^ Data3 ^ Data4 ^ ETX);

    return new byte[]{STX,Address,Data1,Data2,Data3,Data4,ETX,CheckSum};
   }
   
  }

 

public struct Message //Pelco D Message

  {
   public static byte Address;
   public static byte CheckSum;
   public static byte Command1,Command2,Data1,Data2;

 

   public static byte[] GetMessage(uint address, byte command1, byte command2, byte data1, byte data2)
   {
    if (address<1 & address>256)
     throw new Exception("Protocol Pelco D support 256 devices only");
    
    Address = Byte.Parse((address).ToString());
    Data1 = data1;
    Data2 = data2;
    Command1 = command1;
    Command2 = command2;

 

    CheckSum = (byte)(STX ^ Address ^ Command1 ^ Command2 ^ Data1 ^ Data2);

    return new byte[]{STX,Address,Command1,Command2,Data1,Data2,CheckSum};
   }
   
  }

Base Message Format

In both Pelco protocols the bits within the �Data bytes� are broken up into two main groups. For Pan and Tilt commands in Pelco P protocol, the functions are determined as follows:

In order to produce this in C# we should use binary calculation as following:

public enum PresetAction {Set,Clear,Goto}

public enum PatternAction {Start,Stop,Run}

public enum Action {Start,Stop}

public enum LensSpeed {Low=0x00,Medium=0x01,High=0x02,Turbo=0x03}

public enum Pan {Left = PanLeft,Right = PanRight}

public enum Tilt {Up = TiltUp,Down = TiltDown}

public enum Iris {Open = IrisOpen,Close = IrisClose}

public enum Zoom {Wide = ZoomWide,Tele = ZoomTele}

public enum Switch {On,Off}

public enum Focus {Near = FocusNear,Far = FocusFar}

and impelement it like this:

public byte[] CameraSwitch(uint deviceAddress,Switch action)

{

byte m_action = CameraOnOff;

if(action == Switch.On)

m_action += CameraOnOff; //Maybe wrong !!!


return Message.GetMessage(deviceAddress,m_action,0x00,0x00,0x00);



}

But in Pelco D protocol they are quite different:

The sense bit (command 1 bit 7) indicates the meaning of bits 4 and 3. If the sense bit is on and bits 4 and 3 are on the command will enable autoscan and turn the camera on. If the sense bit is off and bits 4 and 3 are on the command will enable manual scan and turn the camera off. Of course, if either bit 4 or bit 3 are off then no action will be taken for those features.

The reserved bits (6 and 5) should be set to 0.

Word 5 contains the pan speed. Pan speed is in the range $00 (stop) to $3F (high speed) and $FF for �turbo� speed. Turbo speed is the maximum speed the device can obtain and is considered separately because it is not generally a smooth step from high speed to turbo. That is, going from one speed to the next usually looks smooth and will provide for smooth motion with the exception of going into and out of turbo speed.

Word 6 contains the tilt speed. Tilt speed is in the range $00 (stop) to $3F (maximum speed).

Word 7 is the check sum. The check sum is the sum of bytes (excluding the synchronization byte) modulo 256.

Extended Command Set

In addition to the �PTZ� commands shown above, there are control commands that allow you access to the more advanced features of some equipment.

For Pelco P protocol the extended command set will have bit 0 of data byte 2 set and will follow the format in the following table:

In Pelco D implementation they are as following:

Please note that in Pelco P implementaiton the checksum is calculation by XOR binary sum of bytes 1-7, but in D one is by madulo 256 sum of bytes 1-6

0A        00001010

88        10001000

Subtotal  10010010  92

90        10010000

Subtotal  00100010  22   (modulo 256 allows the high bit to roll off)

00        00000000

Subtotal  00100010  22

40        01000000

01100010  62  

The response of devices not really important, however just to know that in Pelco P the response will be ACK command, when in Pelco D the response to one of these commands is four bytes long. The first byte is the synchronization character (FF), the second byte is the receiver address, the third byte contains the alarm information and the fourth byte is the check sum.

Good Luck

Feedback

 I would greatly appreciate any comments on how useful you think this software is to you, suggestions for improvements to the overall architecture and/or the efficiency of the base classes, any bug reports, etc.

To reach me, please send all comments to: tamir@khason.biz. As well you can visit my website at http://www.dotnet.us/ to learn more about me.

Open Source License

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If any provision of this Agreement is invalid or unenforceable under applicable law, it shall not affect the validity or enforceability of the remainder of the terms of this Agreement, and without further action by the parties hereto, such provision shall be reformed to the minimum extent necessary to make such provision valid and enforceable.  It is your responsibility to comply with any export laws of your jurisdiction, including without limitation, Israel. This Agreement is governed by the laws of the State of Israel and the intellectual property laws of the Israel. No party to this Agreement will bring a legal action under this Agreement more than one year after the cause of action arose.

If you have any comments, suggestions, improvements, modifications, alterations, derivative works, or other changes (collectively �Contributions�) to the Program that you would like to provide to Tamir Khason, please send such Contributions to: tamir@khason.biz.  By sending Contributions to Tamir Khason, you acknowledge and agree that you grant to Tamir Khason a non-exclusive, worldwide, fully paid-up, royalty-free, license to reproduce, prepare derivative works of, publicly display, publicly perform, distribute and sublicense the Contributions, in source code and/or object code form, and such license is provided by you without any right of accounting.

The copyright notice for the Program is as follows:  Copyright � 2003 Tamir Khason.  All Rights Reserved.  Sponsored by the Tadiran Security Systems ltd.

The contents of those protocols (Not source code or implementation) are considered to be the property of Pelco. Users of this protocol agree to use the protocol only in the interests of Pelco. Any use of this protocol to Pelco�s detriment is prohibited.