How do I get the DSR state property node to correctly read?

[nickj]

I can toggle the DTR line high and
low using a property node for the serial port, modem line settings, DTR line state, and it works fine. However, I cannot get the DSR line to
read properly. Seems to go to unasserted no matter what the input is (and I've verifed the input). I've turned handshaking on and jumpered DTR to DSR (pin 4 to 6 on DB-9), but the DSR line will not read correctly. I'm using 6.1 with Windows 2000.

[Chris_Rake]

This is odd - we frequently use the VISA property nodes for modem line testing and haven't had a problem with 6.1 like the one you describe. Can you create a vi that demonstrates this problems (in the simplest form) and post it? I'd like to take a look at what is going on.

[nickj]

Here's a simple version. Writes and reads to itself fine, and can toggle the DTR high and low. DSR is always unasserted. Thanks for your help.
Nick

[Chris_Rake]

I looked at your code, and it appears that the read of DSR and the setting of DTR are not in a sequence. This will result in unknown order of execution. I suggest that you sequence your VISA vi's by tying the VISA handle output (duplicate VISA resource name) to the VISA handle input of the next vi in the desired sequence.

[nickj]

Good programming point, I attached the new code. However, the DSR still doesn't seem to work.

[Chris_Rake]

Is this on COM1 (built-in) or a plug-in serial port, and is it RS-232 or RS-485?

[nickj]

It's built-in, (COM1), and a RS232.

[Chris_Rake]

I ran your program on my system (900MHz Athlon) and it worked. When I toggeled the DTR switch, the Modem Line Settings: Line DSR State output toggeled as well.

How are you shorting the two pins together? Is it possible that the connection is loose?

[nickj]

Chris,
Thanks for the check, when you let me know it worked on your machine I assumed the computer serial card was going bad. Went down the hall to a Win98 machine that barfed on the VISA resource name, COM1. However, it worked on ASRL1::INSTR. When I entered that name into my Win2000 Dell, the DTR, DSR, CTS and RTS started working, toggling outputs correctly AND reading inputs. So is this a bug? I've used COM1 and 2 on a lot of serial stuff, always has worked but I've never tried controlling the handshaking lines before.