Serial communication using VISA

[Eric Paulin]

Hello everybody,

I need to communicate with a device connected to my COM1 port. I want to use VISA and the data returned by device isn't always the same size but I know what the maximum number of bytes of the data. If I put the maximum number of bytes in byte count (from the VISA read.vi) will it read the data even if it has a smaller size??

Thx!!


Eric Paulin

[jwf]

Use VISA property node set to Serial Settings >> Number of Bytes at Serial port. Wire this value into the VISA read to determine how much to read.

[Stu 708]

You may also want to set up a read till end of line character with timeout that will read a variable number of characters until a CR or LF comes in.
Stu

[Albert.Geven]

Hi Eric
If a device does not send a known number of bytes, it almost always uses an endcharacter.
The only problem with visa is that you have to supply the end caharcter for reading in a property node and inather property node also enable the endcharacter. You need message based settings:termination character and termination character enabled.
Ask for the maximum and the read should stop after the endcharacter.

[SergKr]

Additionally you can read byte by byte in a loop until got the all message you are waiting for.
E.g. I had a stupid device at some time, which was not send any end characters, so I had to wait for the checksum from that device calculating it after each byte received from the device and compare it with last byte 😞

[Eric Paulin]

Hello Sergey,

That's exactly what I have to do :).

Thx!

Eric

[Nikolai Maris]

I use for such cases a while loop, executing every 200 ms (for ex.) and
the functions "bytes at serial port" and "read from port" until the
numbers of bytes is zero.

Niko

Eric Paulin schrieb:

> Hello everybody,
>
> I need to communicate with a device connected to my COM1 port. I want
> to use VISA and the data returned by device isn't always the same size
> but I know what the maximum number of bytes of the data. If I put the
> maximum number of bytes in byte count (from the VISA read.vi) will it
> read the data even if it has a smaller size??
>
> Thx!!
>
> Eric Paulin