flip hex signal

[ollef]

Hi!

I'm using a DB9 contact and re232 to comunicate to a device, the device needs a five byte long signal in hex (2A00 1582 55). However when I send the signal by using labVIEW it gets inversed. I'v tried to invers it by my selfe but no sucess. I'm ading a picture on my signal (top) and the right one (bottom) and as you can se it should also be idel high. How can I flip my signal in LabVIEW?

[RavensFan]

You can't "flip the signal" in LabVIEW.  The polarity of the signal for 0's and 1's is part of the RS-232 protocol.  It is all handled by the serial port.  A zero is represented by a positive voltage relative to ground, a one by a negative voltage relative to ground.

Where are your two displays coming from?  Are you sure you have the polarity of your wiring set up correctly?  Why are you even looking at the raw electrical waveform?

[ollef]

Hi!

I'm trying to design a test jig for a device that has no or at least very little documentation regarding serial port comunication. I have found out what signal to send to the device so that I can conduct my test but it is not working, so I looked at the signal using a USB-6251 and LabVIEW signalExpress and the result was the top signal in the picture (previous post), then I found an old device that can make the same test as I'm trying to do and looked at the signal that this old device sends out (the lower signal). So I'm basically trying to copy the lower signal and then send it out with the help of LabVIEW, but as you can see is the signal inverted in some way and I can't figure out how to change this. I'm also pretty shure that my connections are done correctly.

[Dennis_Knutson · Accepted solution]

It really looks like you are comparing apples to oranges. The bottom signal is not a valid RS-232 signal. The voltage levels are all wrong. If your old device is sending this, you are going to have to do some level translation on the output of the pc's serial port. There is nothing that can be done in software. The UART of the pc is responsible for the voltage levels and they are correct.

[Ben]

Could the signal and rtn be switched? That would flip the sense of the signal.

The first signal does not appear to be referenced to ground. Could that have been captured without a common ground?

Just thinking out loud.

Ben

[ollef]

Thanks for pionting the rs232 problem out, I'm cind of new to the serial comunication and would probably not have realysed that for some time. But we fixed the problem by designing a cirkutbourd that will do the thing for us.