Serial Communication

[K C]

Not everything at once. First get things working with a loopback connector and a basic VI for communication with LV on the COM ports. If you get this working and know what happens in the VI we will do the other things I mentioned.

Do you know how to make this VI ? What version LV are you using ?

[JohnGalt]

I am using Labview 7.0. I should know how to make it, but I have been unsuccessful in it before, so I think with a bit of work I can do it. Pins 2 & 3 are second and third from the top left, I assume? I will look on the labels. I will let you know when I finish it.

[JohnGalt]

OK> I set up the loopback as you said. (I did find pins 2 and 3, they were labeled). I Wrote a program to write an input string to the port and read from the port in an out put string. No matter what I do, I keep getting timeout errors. I even used the example VI's that come with the program. So not even a loopback will get me what I need... I begin to wonder if there is something wrong with the PCI slot that the serial ports are connected to. But that shouldn't affect COM one, since it's not in a PCI slot..... and it doesn't work either. Is my computer just screwed up? It can't be the programming. I used the official stuff even.  What can I try to do to fix this?

[K C]

Hi Cole (is it Cole and not John?),

First you need to check in your windows control panel-system hardware-device manager (depends on windows version) what windows says about your com port(s)

I also made a small VI for a COM port. It is only for a test and not uaseable in a program. I hope you can read it.

Tell me what windows thinks of your COM ports. Are you using WXP?

[K C]

You can also try this with Hyperterminal. Make sure that the flowcontrol is set to none.

[JohnGalt]

So the Device Manager sees all of the ports, but the first four (ME-9100 1-4) give me an error code 10 cannot start. The rest seem fine fro the manager. I tried your VI. For Com 1 it worked beautifully. For the rest, nothing. I think that indicates I need to try something very different with the ME ports. I should try using COM 1 to communicate with the instruments. I will let you know how that goes.

[JohnGalt]

Ok. Tried communicating on Com 1 with the temperature controller. Nothing works. I even tried your VI, KC. It seems odd that it shouldn't work, after i tested it with a loopback and it worked. (yes, it is Cole, John Galt is a character from a book) I will try writing my own, but we all know how successful that has been so far.

[K C]

OK, now we're getting somewhere.  If your instrument works it's OK. But if it not works you have to look if the cable is right.

If it is not working you must measure the voltage at pin 2 and 3 (pin 5 is ground) of the com port from the PC and of the cable from the instrument.

Your PC would normally show at pin2 + or - 8-12V and at pin3 about 0V. Most often the voltage at pin2 will be + if the PC is just switched on and be - if you use or configure the com port.

Do the same with the cable from your instrument. On this connector pin2 and 3 should be the other way (pin2 = 0V and pin3 = +/- 10V)

If this is OK you can plug it in and things could work if not we have to look at the others side.

Message Edited by K C on 10-24-2005 07:59 PM

[JohnGalt]

Sorry, double-posted and removed.

Message Edited by JohnGalt on 10-24-2005 01:31 PM

[JohnGalt]

Ok. Here's going to be interesting for you. I just tested the cords. From COM1, I get somewhere around 10-11v. From the Omega Temperature Controller I get about 7.18v. From the ME card, I get 0.0 v. Never anything but 0.0. I think we may have found the problem, Watson. Thank you. Now, what does this mean. Is it broken, or just different from the normal COM port? Perhaps I should e-mail Meilhaus about this? Progress! Yay! However, when I tried to communicate through your VI with the Temperature Controller on COM 1, it didn't work. Hmmmmm..... interesting.

Thanks very much,
Cole