Pelco D/P protocols

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	Value	Function
1	$A0	STX (start transmission)
2	$00 to $1F	Address
3	Data byte 1	(see below)
4	Data byte 2	(see below)
5	Data byte 3	(see below)
6	Data byte 4	(see below)
7	$AF	ETX (end transmission)
8	$00-$FF	Check Sum

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:

Word 1	Word 2	Word 3	Word 4	Word 5	Word 6	Word 7
Synch Byte	Address	Command 1	Command 2	Data 1	Data 2	Check Sum

The synchronization byte is always $FF.

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

But in Pelco D protocol they are quite different:

	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 Wide	Zoom Tele	Down	Up	Left	Right	Always 0

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:

Command	Data byte 1	Data byte 2	Data byte 3	Data byte 4
Set Preset XX	00	03	00	01 to FF
Clear Preset XX	00	05	00	01 to FF
Go To Preset XX	00	07	00	01 to FF
Flip (rotate 180º)	00	07	00	21
Zero Pan Position	00	07	00	22
Auto scan	00	09	00	00
Stop auto scan	00	0B	00	00
Remote Reset	00	0F	00	00
Zone Start	00	11	00	01 to 08
Zone End	00	13	00	01 to 08
Write char to screen	00	15	0 to 28	0 to 7F
Clear Screen	00	17	00	00
Alarm Ack	00	19	00	01 to 08
Zone Scan On	00	1B	00	00
Zone Scan Off	00	1D	00	00
Pattern Start	00	1F	00	00
Pattern Stop	00	21	00	00
Run Pattern	00	23	00	00
Zoom Lens Speed	00	25	00	00 to 03
Focus Lens Speed	00	27	00	00 to 03

In Pelco D implementation they are as following:

Command	Word 3	Word 4	Word 5	Word 6
Set Preset	00	03	00	01 to 20
Clear Preset	00	05	00	01 to 20
Go To Preset	00	07	00	01 to 20
Flip (180° about)	00	07	00	21
Go To Zero Pan	00	07	00	22
Set Auxiliary	00	09	00	01 to 08
Clear Auxiliary	00	0B	00	01 to 08
Remote Reset	00	0F	00	00
Set Zone Start	00	11	00	01 to 08
Set Zone End	00	13	00	01 to 08
Write Char. To Screen	00	15	X Position 00 to 28	ASCII Value
Clear Screen	00	17	00	00
Alarm Acknowledge	00	19	00	Alarm No.
Zone Scan On	00	1B	00	00
Zone Scan Off	00	1D	00	00
Set Pattern Start	00	1F	00	00
Set Pattern Stop	00	21	00	00
Run Pattern	00	23	00	00
Set Zoom Speed	00	25	00	00 to 03
Set Focus Speed	00	27	00	00 to 03

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  

Final check sum value


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.