byte count

[adeline]

Hi,
i have a voltage increment vi application. i wired a const 50 to my VISA read and it is able to get all the data well. However, when i tried to alter some parts of the vi, it starts to get positive values when i set it to negative values. As a result, when i am supposed to get -230, i get 230.
Is it because my byte count need to be higher? If so, how to we det. how much byte count to set for VISA read?
Attached is the before and after my alteration of my application.
Anyone please help.
ade

[Ricardo_SR]

Hi,

I took a look at the VIs that you sent and for what I understand the changes you do from one to the other shouldn�t affect how VISA reads. If you are sending the same command and you are expecting to read the same as with the first VI, then you should be able to read it with the 50 bytes that you specify in the VISA Read. So, what I think is happening is that by some reason, you are not writing the same command to the instrument and the instrument is the one that is not sending the negative sign. A good way to check or compare what you are sending with one and the other is to use NI-SPY.
You can find it in Windows »Start»Programs»National Instruments»NI-SPY.
This way you can check what you are sending really to
the instrument. The reason for me to believe this is the issue is because on the modified VI, you are trying to read 1000 bytes which is way much bigger than the 50 that you used before, meaning that anything on the buffer would be read.
Hope this helps,

Ricardo S.
National Instruments.