Polling a device connected to the serial port

[Foster Dyche]

I need to poll my machine via serial port.
my code sorta works, I do not use streams or threads.
I have not figured them out yet.
IS there a way to only allow one particular method to run at a time. I think my timer_tick is starting the method a second or more times.

One is there a way to only a method called by a timer_tick to be entered once until that method completes
When the poll is sent with nark parity but the response must be recieved using space parity


Why am I getting multiple lines in the text box from this, should only occur once

I have a program that i am trying to emulate.
in tha program the event only shows up once per occurrance. not many times like my code creates.
I have used a serial port monitor program, for some reason the device is resending the same code again and again even though my app is responding same as the emulated program does.
I am beginning to think that the buffer is not clearing or the parity switching is causing. but when I send commands to the device they work (I have to send the device address (mark) the command with a CRC for all bytes is sent with space parity.

Text box output


$11 door was opened.
$11 door was opened.
$11 door was opened.
$11 door was opened.
$11 door was opened.
$11 door was opened.
$11 door was opened.
$11 door was opened.
$12 door was closed.
$12 door was closed.
$12 door was closed.
$12 door was closed.
$12 door was closed.
$12 door was closed.
$12 door was closed.
$12 door was closed.
$12 door was closed.
$12 door was closed.
$12 door was closed.
$12 door was closed.
$12 door was closed.
$12 door was closed.
$12 door was closed.
$12 door was closed.

 void timer_Tick(object sender, EventArgs e)
        {
            Byte[] GenPoll = { 0x80, 0x81 };
            myserialPort.Parity = Parity.Mark;
            for (int i = 1; i < 50; i++) { } // short delay to allow parity to change
            myserialPort.Write(GenPoll, 0, 2);
            myserialPort.Parity = Parity.Space;
            for (int i = 1; i < 50; i++) { } //short delay to allow parity change
            int bytes;
            string bufferstr; 
            bytes = myserialPort.BytesToRead;
            Byte[] buffer = new byte[bytes];
            myserialPort.Read(buffer, 0, bytes);
            bufferstr = myserialPort.ReadExisting();
            myserialPort.Parity = Parity.Mark;
 
            if (bytes > 0)
            {
 
                    if (buffer[0] == 0)
                    { }
                    if (buffer[0] == 0x01)
                    {
                        textBox1.Text += "$01  Ack\r\n";
                        buffer[0] = 0x00;
                        myserialPort.Parity = Parity.Mark;
                        for (int i = 1; i < 50; i++) { }
                        myserialPort.Write(GenPoll, 0, 2);
                        myserialPort.Parity = Parity.Space;
                        for (int i = 1; i < 50; i++) { }
                    }
                    if (buffer[0] == 0x11)
                    {
                        textBox1.Text += "$11  door was opened.\r\n";
                        buffer[0] = 0x00;
                        myserialPort.Parity = Parity.Mark;
                        for (int i = 1; i < 50; i++) { }
                        myserialPort.Write(GenPoll, 0, 2);
                        myserialPort.Parity = Parity.Space;
                        for (int i = 1; i < 50; i++) { }                       
                    }
                    if (buffer[0] == 0x12)
                    {
                        textBox1.Text += "$12  door was closed.\r\n";
                        buffer[0] = 0x00;
                        myserialPort.Parity = Parity.Mark;
                        for (int i = 1; i < 50; i++) { }
                        myserialPort.Write(GenPoll, 0, 2);
                        myserialPort.Parity = Parity.Space;
                        for (int i = 1; i < 50; i++) { }
                    }
 

[arie]

There are three different timer classec in c#, if you use them in a wrong way it can really hurt. This articles explain the differences:
http://msdn.microsoft.com/en-us/magazine/cc164015.aspx
http://intellitechture.com/System-Wi...-Timers-Timer/

Since your timer has an event called "Tick", I guess its System.Windows. Forms.Timer, which is supposed to be used only for interactions with Forms.

Is using a timet the best choice? Have you thought about using DataReceived event of the SerialPort object?
http://msdn.microsoft.com/en-us/libr...areceived.aspx

Althought its description is not very reasuring (for example "Because the operating system determines whether to raise this event or not, not all parity errors may be reported." and so on...) but once you get it to work, it works.

To detect parity errors, you may also want to subscribe to ErrorReceived event
http://msdn.microsoft.com/en-us/libr...rreceived.aspx

Also, I had never tried to change the port's parity when it was open, so I don't know if it causes problems

About your timer running before the previous finnishes processing.
I suppose you can use locks to ensure your timer's method runs "one at a time". And are you sure you subscribe to your timer's Tick event only once?

Sorry about all this, a bit incoherent, rambling :) Actually I just finnished a project similar to yours, I had to ask serial port for data periodically, receive the responses and process it. I used Elapsed event of System.Timers.T imer object to ask for data (write to the port), DataReceived event of SerialPort to receive answers (read from port, this part was a bit tricky, e.g. I used Thread.Sleep() method to wait for all data to come, which - theoreticaly - I shouldn't do; but it works) and then I did all time consuming data processing (like printing, comunication with databases) using BacgroundWorker s.

About how DataReceived event works: http://social.msdn.microsoft.com/For...-adff82b19e5e/

[Foster Dyche]

If I use the DataReceived Event
The machine will not send anything until 5 seconds has elapsed since the last transmission from host computer, at that time it starts sending its address to the host.
It thinks the communications link is broken.

The communications protocol is designed to work with RS485 and Fiber optic as well.

I know the program that I am trying to write my own version, becasue it lacks a database, polls the machine.
I can tell that by the data captured with a serial monitoring program.

I suspec it was done in 2001-2002
I just wish I could figure out what they used to code it and what libaries they used.

[arie]

Are you sure it is not some sort of hardware problem? What kind of connection is it? Do you use RS-485 and some sort of converter or something else?

Do you know what exactly and when exactly is sent/received by your program and at what time? There is virtual serial port emulation software that can intercept your data, so you can see what's going on. (I used it, but it was someone else who installed it so I dont realy remember what was it called).

That's how I found out what was causing my problem: I asked my device for data, then, sometimes, it wasn't responding for few seconds (or even a minute). It turned out my data was sent/received correctly by the device, but the converter1 (connection device <> RS-485 <> converter1 <> LAN <> converter2 <> RS-232 <> host PC) was malfunctioning and it was holding baches of data randomly.

From my experience, DataReceived event usually is received just fine and it's usually something else at fault (programming or hardware problem).

Does your communication protocol include some sort of "end of message" byte/character? If so, I've seen solutions on the Internet that:
- use timer to ask for data
- use DataReceived event and, within its method, Read(buffer, 0, bytes) or ReadExisting() method to receive data and put it into a buffer.
- buffer is a global variable that is processed outside of DataReceived by some sort of queue and BackgroundWorke r, or by another thread. Messages are distinguished using "end of message" byte/character.

[Foster Dyche]

I was saying the protocol can use R232, RS485 and fibre.
the machine has all 3 available on it's comm board
I have used both Advanced Serial Port Monitor(AGG) and Free Serial Port Monitor (HDD) to watch the port. I have the machine configured to use RS232
The software i am trying to code so I can use my own) warns that it may have communications issue, but it never has that I noticed.

Using the monitor program I noticed it thinks the port is configured 8 data bits and 2 stop bits. I should try running Advanced Serial Port Monitor on it again

The software I am trying to copy sends out 0x80 and (0x80 OR'ed with address) both with wake up bit set) the machine will then send a response no wake up bits set)
If the software has a commmand for the machine it sends the address (0 to 127) with wake up bit sst, then the command/instruction/data and a custom CRC with no wake up bits.

The only time the machine asserts a wake up bit is when it thinks the link is broken, not getting polls from the host.

there is no special end of data character sent (depending on the response the packet size will vary from 1 byte to 16 or so.
the only 1 byte I see is the Ack from the machine for some commands
the host has to send at least 4 bytes out for command/request.
Example
0x01 0x50 0x12 0x24 outbound could be address (wake bit) shutdown and 16 bit CRC these are example bytes the machine responds 0x01 if it got the command no wake up bits.

It is getting framing errors
Default replacement is 3F I changed it to 00, until I can figure out how to make drivers, OS and .NET Framework ignore the framing error, which might solve my issue.
if I get a bad byte oh well, the crc will fail and either the host or machine will re-transmit.