Serial Read doesn't read all available characters

[sealy0910]

Hi,

   I am trying to communicate with a Magellan/Ion controller using RS 485. I am running an external device monitor with shows me that 7 bytes are sent from the controller to labview, I am using the basic VISA Write then wait a few milliseconds and then VISA Read  as well as using the property of bytes at port to tell the VISA read how many bytes to read. When I look at NI Spy I can see that the VISA read function is told to read 7 bytes from the right COM address but only six bytes are read. I have changed the delay before read time from 0 to so long that it doesn't read anything and I still have the problem. Is there a timeout or maxium number of bytes that the VISA read has internally that I am running into or is there some other fix to my problem?

[Albert.Geven]

Do you have endcharacter dtection enbled and is your endcharacter lost or some other character?

[sealy0910]

Termination charater is on since it is the default setting. I strange thing about this is that i have 13 commands  that i write to the controller and then read back the responses. It is only the one which requires 7 bytes to be read back that has any trouble.

[Dennis_Knutson · Accepted solution]

It's not strange at all. It is expected. If you are not reading ASCII, then disable the term character. VISA read terminates as soon as the character is detected.

[JB]

Yes, this is expected ! See here for more details about termination characters in NI-VISA.

[sealy0910]

Thanks so much for everyone's help. That was the exact problem. Being new to labview these disscusion forums are very helpful.