I am trying to send "00000000" (aka. null value) in the serial port

[GaryZ21]

I am trying to send a null character in a string out to the serial port through asynchronous transmission, using CVI 7.1.  The null value is the very first character in the string.  Is there a way to have the serial driver send that value out?  Below is a section of my code. 


 Fmt(cDataPacketW, "%s<%c%c%c%c",     cWord[1], cWord[2],cWord[3],cWord[4]);               
cmd_written = ComWrt (comport_A, cDataPacketW, 4);
ProcessSystemEvents();                                    


The first character cWord[1] has a value of "0".  However, when I try sending out the string, I get 0 bytes written. 

[RobertoBozzolo]

Could you try this modified lines?

cDataPacketW[0] = cWord[1];

cDataPacketW[1] = cWord[2];

cDataPacketW[2] = cWord[3];

cDataPacketW[3] = cWord[4];

cmd_written = ComWrt (comport_A, cDataPacketW, 4);

Or simply, supposing cWord is a character array,

cmd_written = ComWrt (comport_A, cWord + 1, 4);

Message Edited by Roberto Bozzolo on 02-16-2006 07:07 AM

[CVI-User]

If it is "char cWord[]" and cWord[0] = 0, but you want to write ASCII '0'  you have to do

Fmt(cDataPacketW, "%s<%c%c%c%c",     cWord[1]+'0', cWord[2]+'0',cWord[3]+'0',cWord[4]+'0');

because you now just write an 'empty' string (cDataPacketW[0]==0) and hence get 0 chars written.

[RobertoBozzolo]

Well, he could simply use

Fmt (cDataPacketW, "%4c", cWord + 1);
cmd_written = ComWrt (1, cDataPacketW, 4);

But, Gary, I tried with your exact code and get 4 bytes written, so in my opinion the problem lies elsewhere.

Message Edited by Roberto Bozzolo on 02-16-2006 10:23 AM

[GaryZ21]

Thank you all for the very quick reply.  I forgot to post a line I had in my code to the earlier message.  I used "stringsize = StringLength (cDataPacketW)", to determine the size of cDataPacketW and placing that value into the comWrt() function.  I corrected the code by placing an if statement to monitor that none of the cWord was an ascii null, and default the write size to x - 'size of string'.  Thanks again.

[Joseph.han]

Hello GaryZ21 ,

Did you solve this problem at this moment.

I also face this problem now.  I can not convert the 0x81 0x81 0x00 0x00 0x32  to correct  string. just received the first two words, because the string define the 0x00 is the end of string char.

If you solved this problem, Could you show me how to do? Thanks.

[RobertoBozzolo]

Joseph, the most probable cause of your problem is some function detecting the nul byte as and-of-string and  stopping there. We could be able to help you if you post the part of your code in which you are preparing the string to send to the com port, including variable definitions.

Message Edited by Roberto Bozzolo on 12-21-2006 07:01 AM

[Joseph.han]

Hello, Roberto Bozzolo

Thanks for your reply.

I want to communicate with one equipment with RS232 port  and sent out  those command.

Below is some parts of my program. Pls help me to check how to do for this string.

"

 char Commands[10];    //define
        Commands[0]=0x81;
        Commands[1]=0x81;
        Commands[2]=0x52;
        Commands[3]=0x00;
        Commands[4]=0x00;
        Commands[5]=0x00;
        Commands[6]=0x53;
        Commands[7]=0x00;  
   
 OpenComConfig (1, "", 9600, 0, 8, 2, 512, 512);
 ComWrt (1, Commands,strlen (Commands));
 Delay(0.2);
 Read_Count = GetOutQLen (1);
 Delay(1);
 ComRd (1, Read_Buffer, 10);

"

[RobertoBozzolo]

You are having problems due to the use of strlen () instructions that stops at the first nul byte it finds. To transmit all bytes in the buffer you need to pass the exact number of bytes to ComWrt function: in your case this statement should work correctly:

ComWrt  (1,  Commands, 8);

[Joseph.han]

Hello, Roberto Bozzolo

Thanks again.

Now it's working.