Problem in using serial port.

Question

I am using serial port to get data from a fusion splicer. The number of bytes at the port is 4096 but the read buffer of VISA read is empty. I am reading the same number of bytes. Can any one tell me what is the maximum size of VISA Read buffer? I am trying to put the contents of the buffer in a file. I am using labVIEW 6.1 on linux.I am also attaching the VI.
I also noticed this problem...If I read the number of bytes in the serial buffer many times, sometimes it reads it as 0 and I have to keep trying until it reads this 4096 bytes.
Thanx for any help.
S.Vijayalakshmi
Attachments:
serail_comm.vi ‏52 KB

Answer 1

Hey Viji,
In your application it looks like you are just checking to see how many bytes are at the serial port. Is it possible that your application is check for the serial data at the port before the data actually gets there. If you are looping this code as a subVI or just running it over and over it is possible that one of the iterations could occur faster than your device can write the information to the bus. In this instance you are checking the number of bytes at the port and there might not be any there yet. In this case the port reads 0 as you have designed it.
If you want the read function to wait and always read 4096 then don't wire the bytes at port to the read function. Just wire a constant/control equal to 4096 to the read function instead o
f the bytes at port. In this case, if there are not any bytes at the port the read function will wait for the bytes to show up or until the timeout period is reached.
I would also, suggest lowering your time to something more reasonable, because if your instrument quits transmitting your application is going to wait for 33 minutes. That is a long time for a program to hang.
I hope this helps out.
JoshuaP
National Instruments