My device is attached on serial port(COM1). I wrote a code and in this first I pass one command to the device( write comand on device) and then read it. I checked settings for serial port but didnt find any thing wrong with that. but it's always giving me the error " -1073807339. VISA Read in testing.vi".. don't know what's the problem. I changed time out by a factor of 100 but still..My device is "NEWFOCUS's model 8753" I am also attaching the file. So you can have a look at the code too. I tried time out too. and I tried various termination character too. though in the manual they didnt mention any termination char.