ComWrite in labwindows

[ammukrish]

Hi,

I am facing problem in writing hex data to com port using ComWrite.  How i will make sure that whatever data sent is written to my target properly because i am not seeing any changes in my target.

Whenever i am trying to read data from my target which is continously sending some response i can read through comRead successfully but write doesnt goes well. I cross verified the same message with other termnial where i can write hex data. but in CVI i cant. your feedbacks are much appreciated.

int no_of_bytes=0;

char comdata[100] = {0x28,0x00,0x02,0x00,0x01,0x00,0x01,0x00,0x00,0x00,0x29};

no_of_bytes = ComWrt (COM_PORT, comdata, strlen(comdata));

thanks.

[RobertoBozzolo]

The proble is in the use of strlen () to calculate the number of bytes to send: strlen treats c-like strings, that is it will return the position of the first NUL bite in the string: in your case it will return 2 bytes instead of 11 you are expecting.

The only solution is to calculate this number in a different way.

[ammukrish]

Thank u very much.

now i have written my code as 

no_of_bytes = ComWrt (COM_PORT, comdata, 11);  and it works.

instead of couting the number of bytes manually is there any way where we can get count of number of bytes?

[RobertoBozzolo · Accepted solution]

Since you are dealing with raw data, there is no way to discriminate the number of bytes to send: each byte could theretically assume ever value fro 0x00 to 0xFF.

Unless your protocol has some characteristics you can leverage on (e.g. some end-of-transmission character or 7-byte protocol) I see no way other than counting bytes while you are preparing the message to send.