VISA read and write issues

[zahidkjatoi]

Dear LabVIEW Champions,

I have a device with Serial communication. I have written a program to read and write (give command) to the device using VISA. I have to continously read and write according to some other Parameters.I have attached 3 VI's for reference. The Problem is described below.

1. When I write (give specific temperature ) to device, it successfully accepts it and Change the temperature. But when I read it gives me the value which I recently write (give command). It does not Show me current temperature of device.

2. After one or two times, it Shows me 0, when I try to read the temperature.

3. If I do not write, it gives me correct read values. But when I write and then read... it gives me wrong values.

Hopefully I could explain the Problem.

I am looking Forward for meaningful reply.

Thank you so much in advance.

Khan.

[RavensFan]

First of all, don't use bytes at port.  Your device seems to be using a termination character, at least your initialize subVI sets up the connection to use one, so take advantage of it.  When you do a VISA Read, wire in a number of bytes larger than the longest message you expect to get.

Can you attach the VI where you put all of these subVI's together into a bigger program.  It is hard of us to know how you are actually using them.

Have you read the manual?  Most devices have a command response format.  So if you send a command, the device responds back.  I would expect a command that tells a device to set a temperature to respond back with a message that says what temperature it was set to.  I would expect there to be a different command to write to the device if you want a message back that tells you what the current temperature is.

[crossrulz]

What exactly is the device you are trying to communicate with?  Is there a manual you can link us to?  There are likely details in the communication protocol that you are not quite understanding which can cause all kinds of issues.