topic Re: RS232 communication problem in LabWindows/CVI

RS232 communication problem

Geert Van Doorselaer — Wed, 12 Sep 2001 09:05:51 GMT

Hi all,

I try to read out the data of a METEX M-3850D multimeter in a LabWindows CVI
program (5.0.1).
These are the communication parameters:
1200 baud, 7-bit ASCII, no parity, 1 stop bit.
I use serial port 2.
After sending the characters 'D' and 'enter', the multimeter should respond
with a 14-character frame.

This is the code I use:

int numbytes;
char buf[512];
OpenComConfig (2, "", 1200, 0, 7, 1, 512, 512);
SetCTSMode (2, LWRS_HWHANDSHAKE_OFF);
FlushInQ (2);
FlushOutQ (2);
numbytes = ComWrtByte (2, 68);
numbytes = ComWrtByte (2, 13);
numbytes = ComRd (2, buf, 14);
CloseCom (2);

This is the problem: after the instruction OpenComConfig, the RD line is
pulled high (+15V) by the computer, resulting in a logical 0 and thus
blocking the port. Wi
th a scope, I can clearly see that the multimeter is
responding its 14 characters, but as this results only in a 0.5 volt signal
superimposed on the +10 V, the computer is of course unable to read this
data.
Only after about 5 seconds after calling the ComRd instruction, the RD line
is released.
There are no problems with the TD line.
When the multimeter is unplugged, the same thing happens (except the
response of the multimeter of course), so I blame my program, my serial port
or LabWindows.
Changing the SetCTSMode does not help.
What could be the problem?

Kind regards,
Geert

Re: RS232 communication problem

Farid Bengrid — Wed, 12 Sep 2001 12:53:34 GMT

Try the following:

int numbytes;
char buf[512];
OpenComConfig (2, "COM2", 1200, 0, 7, 1, 512, 512);
FlushInQ (2);
FlushOutQ (2);
sprintf(buf,"D\r");
numbytes = ComWrt (2, Buf, 2);
numbytes = ComRd (2, buf, 14);
CloseCom (2);

Best regards.
Farid.

Re: RS232 communication problem

Geert Van Doorselaer — Wed, 12 Sep 2001 14:05:58 GMT

"Farid Bengrid" wrote in message
news:5065000000050000004E410000-999158726000@exchange.ni.com...
> Try the following:
>
> int numbytes;
> char buf[512];
> OpenComConfig (2, "COM2", 1200, 0, 7, 1, 512, 512);
> FlushInQ (2);
> FlushOutQ (2);
> sprintf(buf,"D\r");
> numbytes = ComWrt (2, Buf, 2);
> numbytes = ComRd (2, buf, 14);
> CloseCom (2);
>
> Best regards.
> Farid.

Thank you for your input, but the results are just the same ...

Best regards,
Geert

Re: RS232 communication problem

Farid Bengrid — Wed, 12 Sep 2001 14:31:59 GMT

Hi geert,

Did you try with hyperterminal ?

Best regards,
Farid.

Re: RS232 communication problem

Geert Van Doorselaer — Wed, 12 Sep 2001 15:36:02 GMT

> When the multimeter is unplugged, the same thing happens (except the
> response of the multimeter of course), so I blame my program, my serial
port
> or LabWindows.

This is not correct. It is indeed the multimeter that messes up its own data
transmit line (which is the PC data receive line). So I will start reverse
engineering which command is still missing to put the multimeter in its
appropriate mode.

Sorry for bothering you. Thanks for your inputs and your time, Farid!

Geert

Re: RS232 communication problem

bman — Thu, 13 Sep 2001 20:21:02 GMT

Geert

Try this small example program to see if you can communicate with your multimeter correctly. If you have the same problem with this program, let me know.

Brian