Serial Communication

[Dennis_Knutson]

I wouldn't worry to much about using MAX, especially if you can't get Hyperterminal to work. MAX won't do anything more than detect whether you have a com port in your pc. It won't try to communicate with your instrument, it won't try different baud settings, etc. You have to do all of that yourself and if you guess wrong, there's no communication and NI-spy won't help either. I was really hoping that you would find a cable problem. Have you tried Hyperterminal with one of the built-in com ports on your pc (i.e. com1 or com2) or tried it on a different computer? Frankly, I'm running out of ideas. You might try enlisting the help of your local NI Sales Engineer. He or she might be willing to help you out or put you into connect with someone local that could help. If one exists, a local LabVIEW user group could also be a great resource.

[unclebump]

What is the exact part number of the MDSi8?? Some of them don't have communication builtin. The datasheet says it can do modbus protocol. Normally that uses 9600 baud, 8 databits, even parity, one stop bit. The communication manual states that the meter does not use the parity bit. There are several vi's that implement Modbus serial communication. I have some at work that I can send.

Here is a link to the MDSi8 manual. http://www.omega.com/manuals/manualpdf/M3944.pdf This shows you only need three wires in the serial cable. Wire pins 2-2, 3-3 and 5,5.

Here is a link to the I Series communication manual. http://www.omega.com/manuals/manualpdf/M3397.pdf

When talking modbus with the device you can use function codes 3(read holding register), 4(read input register), 6(write holding register), 8(diagnostic). The meter has up to 43 registers, but not all of them are used.

[unclebump]

Here is the 937 communication manual. http://www.mksinst.com/pdf/HPS937-232-485man.pdf

The 247 doesn't have an rs232 port.

[xseadog]

Hi John

You said that now the scope is also serial comms well start there! Disconect all other serial connections. Connect Scope to PC serial port. Initialise MAX, also NI spy (set to capture), with MAX

do a instrument search on your serial ports. Remember that scope you should be switched on !! MAX should be able to see scope, as Dennis mentioned if necessary alter the port settings. Check with the scope manual to see what the default setting are. In MAX you can test basic functions ie send IDN command to check scope ID.

Hopefully this should set you on ya way- also verifies that you serial ports are functioning ( swop connections to test all ports)

xseadog

[Dennis_Knutson]

Just a bit of clarification. You cannot do an instrument search for the serial ports. MAX will only find the com port itself. It will not find or attempt to find any instrument connected to a serial port.

[K C]

Hi John,

Is your problem solved ?

If not let me know, we can go through the whole process (begin to end) to get things working.

[JohnGalt]

I shall try the starting over with the scope. However, that will be a while. The Computer it has been running on is going away for a few days to do experiements elsewhere. But that sounds like it at least has a chance of working. I am afraid we are all running out of ideas. I have spoken to the "official" people at NI and even they can't figure out why this isn't working, he recommended this forum. I will make sure to test it in all ports.

Thanks again, see you in a few days.

[JohnGalt]

My problem is not near solved, but I am going to try to do the whole thing over to see what we can do. I will leave the old program intact, but start doing the Oscilloscpe on another program and work from there. Hopefully something will happen.

[K C]

Hi John,

There are a lot things said in this thread and I think your right. Better start again at the beginning

Suggestion to get things solved:

First you have to get a basic LV VI running on your COM port with a loopback connector. A loopback connector just connect pin 2 and 3. The only thing you need is a working COM port, loopback connector and VI

Next you have to make a cable with or without cross. You can measure this.

Last (but not least) setup the communication with your instrument.

Is this workable for you ? What can you do yourself and where do you need help?

Message Edited by K C on 10-19-2005 08:59 PM

[JohnGalt]

OK. I think I can get a loopback connector worked out. I will trysending and reciving data in Labview through this. I think I tried it before, but I am not sure I understood it then. I will also try this on the pre-installed COM port on my computer. I can't get that to communicate either.What do you mean by make a cable with or without cross? The cables I am using have been tested, so that is not the issue I don't think. What did you want me to measure aboutthe cables, though?

Thanks for the advice,
Cole