LabVIEW
Can I send ASCII Stream with TCP-Write?
@evila wrote:
Thank you for answering!
I'm not still sure that LV sends messages in ASCII text from. Are you sure, that there is no binary form conversion between those Active and passive vi's?
I'm thinking that TCP write converts ASCII to binary (before sending) and then TCP read converts it back to ASCII format in that another vi.
There is no difference between binary and ASCII as far as the stream itself in LabVIEW is concerned. In fact TCP/IP also makes no difference at all. It is always a stream of bytes, independant if there happen to be readable characters in there or simply some random or not so random binary data bytes.
The only difference you have in some higher level protocols such as FTP is about how to treat special characters such as carriage returns and line feeds. LabVIEW does nothing of this on its own, you specifically have to include any carraige return and/or line feed you want to send. One convinience option LabVIEW has is the mode parameter of the TCP Read function, which can be set to CR/LF and that means that LabVIEW will terminate the read as soon as either:
1) the requested amount of bytes have been read
2) the timeout has expired
3) a carriage return/line feed pair has been received
This mode allows to easily support line oriented protocols, as there are many of them built on TCP/IP.
But inherently an ASCI string is simply an array of bytes as well and therefore you can always transport ASCII strings through a binary stream but not vice versa.
If you want to send ASCII strings it is likely that you will also have to add the cr/lf characters to them and in LabVIEW you have to do this explicitedly, as LabVIEW will not do any implicite ASCII->binary conversion at all as you seem to think.
Rolf Kalbermatter
Message Edited by rolfk on 06-21-2005 06:10 AM
@evila wrote:
Yes, the client application is written in Envision/Igrip program with Graphic Simulation Language (GSL) (a programming language developed by DELMIA)
I'm reading information from USB joysticks with LV (server) and the data should be send to the client. I can establish a connection between server and client, and I can also send data from client to LV server, but I can't read data form LV with my client application. I'm using normal TCP/IP read write routines in LV.
Here is the LV server vi, maybe here is some problems with my vi.
Most probably your client is waiting for a carriage return and/or line feed before proceeding to decode the command so you will have to append that to the string before passing it to TCP Write. Just as mentioned in my earlier post.
Are you really sure the client expects a binary 32 bit integer first, telling it the number of bytes? Looks a little strange considering that everything else is completely in ASCII. If it really does expect a binary 32bit integer you will have to investigate if this is supposed to be in big endian or little endian. Chances are for applications developed on Intel x86 CPUs that they expect little endian, but LabVIEW and also most network applications do expect big endian instead. You can change the endianess by wiring the integer value through Swap Bytes and Swap Words from the Advanced palette, before typecasting it to a string.
Rolf Kalbermatter
Message Edited by rolfk on 06-21-2005 08:24 AM
