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C# Serial Port Communication

Posted on 2009-07-09
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Last Modified: 2013-12-17
Im trying to communicate with a device via serial but am having a hard time understanding the protocol.  I am not too familiar with serial communications.  

Below is some of the protocol format:

Each protocol should follow the same format as below

SYN, SYN, STX, SA, CM, CD, XXXX, CS, ETX

Where:
SYN - Is sent in hex ($16)
STX - Is sent in hex ($02)
SA - Is the device Address sent as a hex
$07 = device #7
$1E = device #30
CM - Is the command sent as a HEX
$00  Normal (display)
$01  Display FULL
$02  Display OPEN
$03 - Display CLSD
CD - $00  Disables checksum (For one way communication)
$01  Enables Checksum
XXXX - Is the four digit number as ASCII (Note: preceding zeros must be present)
CS - Checksum is sent as HEX (see checksum routine)
ETX - Is sent in hex as ($03)

The checksum routine uses the XOR command on all significant data to ensure data
has not been corrupted. By using the following routine a checksum should be created
and transmitted with the data being sent.
SYN, SYN, STX, SA, CM,CD, XXXX, CS, ETX
Step 1: temp = SA XOR CM
Step 2 : temp = temp XOR CD
Step 2: temp = temp XOR X(1)
Step 3: temp = temp XOR X(2)
Step 4: temp = temp XOR X(3)
Step 5: CS = temp XOR X(4)
The control module will repeat this calculation and the results will be checked. If and
only if the results of the checksum match, and the sign address matches the field set
address will the data be displayed.
Example:
For sign 1 to display 0017 with a checksum being used the packet would be:
Bytes that are included in checksum calculation
$16, $16, $02, $01, $00, $01, 0, 0, 1, 7, $06, $03

If the data has been verified by the correct
unit, that sign will transmit:
SYN, SYN, STX, ACK, ETX
Where:
SYN is sent as hex ($16)
STX is sent as hex ($02)
ACK is sent as hex ($06)
ETX is sent as hex ($03)

Examples:

PACKET:
$16,$16,$02,$11,$00,$01,1234,$14,$03

PACKET:
$16,$16,$02,$11,$01,$01,0000,$10,$03



Can someone provide me with some sample C# code that will format a packet in this format to be sent to the device?
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Question by:Alldaypilot
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Jens Fiederer earned 300 total points
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Assuming the commas are just there for display,

    private byte[] DoFormat(int sa, int cm, bool ck, int num)
    {
        byte[] packet = ck ? new byte[13] : new byte[12];
        int index = 0;
        packet[index++] = 0x16;
        packet[index++] = 0x16;
        packet[index++] = 0x2;
        packet[index++] = (byte)sa;
        packet[index++] = (byte)cm;
        packet[index++] = (byte)(ck ? 1 : 0);
        string digits = string.Format("{0:X4}", num);
        for (int i = 0; i < 4; i++)
        {
            packet[index++] = (byte)digits[i];
        }
        if (ck) {
            packet[index] = 0;
            for (int i = 3; i < index; i++) {
                packet[index] ^= packet[i];
            }
            index++;
        }
        packet[index++] = 0x3;
        return packet;
    }

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by:Alldaypilot
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All I really need with this is a code example of how to send out a serial communication command using this format and receive what the device is sending back.


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Expert Comment

by:Jens Fiederer
Comment Utility
A sample of how a packet is actually sent is in the MSDN samples.
You can get those at

http://msdn.microsoft.com/en-us/library/c8zc5kah%28VS.100%29.aspx


Note that depending on the nature of the device you are addressing, you might need hardware to convert your serial port (not if you are talking to a normal async RS-232 port, but the nature of the packet suggests you might be addressing a syncronous or poll-select device).
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Author Comment

by:Alldaypilot
Comment Utility
Thank you jensfiederer.  I will give it a shot and see if that works.
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Author Comment

by:Alldaypilot
Comment Utility
Would I send it to the device like this:

port.Write(packet, 0, packet.Length);


I connect to the device and the receive led lights when I click send but the message is not changing still.
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by:Jens Fiederer
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Yes.
Do you know whether you have the baud rate, start bits, stop bits, parity settings all correct?  All of these are needed for successful async communication.

And, as I said, if your device is NOT async RS232 you might need special hardware.
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Author Comment

by:Alldaypilot
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This is from the documentation:

Our display unit is set up for 9600, N, 8, 1 serial communication. In
addition, each unit is field addressable for a total of 255 signs to be operated off of
one system

And here is what I am using:

  SerialPort port = new SerialPort("COM1", 9600, Parity.None, 8, StopBits.One);



I will have to check into the asynch RS232 because it doesn't mention that anywhere.

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by:Jens Fiederer
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Looks good, actually.  
Any hardware flow control that could be holding you up?
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Author Closing Comment

by:Alldaypilot
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I still have not been able to get this device to communicate but I think it is partially at fault for poor documentation.

jensfiederer pointed me in the right direction on how this should work.
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by:Jens Fiederer
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Thank you for coming back to the question.
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