The equipment has moved out of the lab and into the field. Everything is wired up and it appears that I'm failing to communicate with the 7017s more often than not.
One 7017 is adjacent to the PLC, one is about 50ft away, and one is +100ft away. The two furthest 7017s have biasing and pull-up resistors installed.
I got rid of the part of the code which, after complete failure to connect to a 7017, it would stop trying on later cycles. The result is that I /sometimes/ get successful connection and sometimes fail. I added an "attempt" counter and a "failed" counter to calculate the success rate, so I'll have that statistic next time I make it on-site.
Elsewhere in Tech Support it was suggested to use the U-485 to watch the RS485 communication as it's happening. I have purchased a U-485, loaded the driver and my computer is recognizing it. I also loaded up the Realterm SourceForge terminal software I saw suggested elsewhere in TechSupport
http://realterm.sourceforge.net/. From reading the SourceForge website, I think I want to "Spy" the communication. When I try that in the office (nothing wired up) I get a pop-up demanding a donation ($20) before I can use this option. Is this the option I need, or should I use "Monitor"?
Once on site, I will wire up the U-485 as shown here:
http://www.tri-plc.com/drivers/U485-Drivers2009forCP2102/CP210xSetupGuide(English).pdf on page 3. (I wont be using the 120Ohm resistors.) What isn't shown is the relative location of the PLC. If I have occasional success communicating, can I wire the U485 directly to the COMM port on the PLC (without resistor) to do the spying? Aren't the needed resistors and pull-up stuff already there for comm with the plc?
So, assuming I make it that far, what next?
If I need to use "Spy" then I click the "Ports" tab, set the Baud to 9600 (default for PLC and what my 7017s are set for) and make sure the port is set to match the location of the U485. There are many other options to select at this tab and I don't know what the rest of it means, so
if there is more to do, please let me know. At some point I'll click the "Spy" button and, if I've made my donation, /something/ will happen.
What will happen? and what does it tell me?
My plan is to go on site as soon as I have a clear plan of troubleshooting. Right now I'm unclear on how to use the U485 to troubleshoot.