SeriaConnection to MicroLogix controller- help!

Hello,
As my user name implies - I am totally new to the wonderful world of PLCs. I have though been tasked with integrating into our larger software package a connection to MicroLogix 1400 controller so that we can simply read/write specific registers. Connection will be via RS232 serial connection. For connection software, I have used https://github.com/robertlarue/DF1Comm/blob/master/DF1Comm/DF1Comm.vb - which is straightforward, with routines which could be easily combined with our software. For serial connection I am going from COM1 port of PC to (9-pin) serial port of MicroLogix controller via null modem cable (wiring as per http://www.home-machine-shop.com/bits/NULL_MODEM_CABLE.jpg). Controller is set to default communication config (19200 baud, no parity - Node is "1").

When I try "autodetect" (which sends DLE -ENQ, varying baud/parity/etc pms to get reply) to make initial connect - I get no response at all. I do not see COMM 1 indicator on controller flash. I know that I am sending out bytes thru port, because if I connect pins 2/3 (send/receive) -I can see echo using terminal emulator on COM1.

Is there something obvious (or not so obvious...) that I may be missing, or something else that I might try? I see that I might try RSLinx software - but I think that if cannot make connection right now - that package will not help me.

One additional point which I just noticed. On my (Windows 10 PC) - if I connect COM1 to COM2 and write thru COM1 - I see echo of out bytes in COM2. On the Windows 7 PC which is connected to controller - with same config, I do not see echo (even though if I cross over pins 2 and 3 - I get echo...). (Is there difference between serial writes?). Unfortunately - I can only connect to controller via Windows 7 machine right now.

Thanks to all for any help or ideas..

Which MicroLogix (1xxx, 8xx)?


I would not expect an echo from the PLC; it's not the TTY on a Linux box.

Try RSLinx... if your cable is correct and your settings are correct you should be able to see the processor in RSLinx, once you get that working you can go onto your other software.

You should be able to do something like this http://www.youtube.com/watch?v=QIu1AGUR4N8

That video is using my USB adapter so you can just leave it set as COM1 and click auto configure

1766-L32xxxx

drbitboy said:

Which MicroLogix (1xxx, 8xx)?

Click to expand...

Total_newbie said:

MicroLogix 1400 controller

Click to expand...

Thanks. I am trying to install RSLinx now, and will give that a shot...

Thanks to all for the ideas. It turns out that problem was with serial port on the Windows 7 PC which I was using. Either port is not (completely) working (it was working enough though that I was getting echo when I jumpered pins 2 and 3), or somehow pins are mixed up. (I don't know how that might occur...). Just trying to connect and read registers though with my Win10 machine (getting it to controller was no easy task... why can't they make laptops with serial ports?) - worked beautifully on 1st try. A 3 day learning experience...

Total_newbie said:

worked beautifully on 1st try. A 3 day learning experience...

Click to expand...

glad you got it and welcome to the club!

Total_newbie said:

Thanks to all for the ideas. It turns out that problem was with serial port on the Windows 7 PC which I was using. Either port is not (completely) working (it was working enough though that I was getting echo when I jumpered pins 2 and 3), or somehow pins are mixed up. (I don't know how that might occur...). Just trying to connect and read registers though with my Win10 machine (getting it to controller was no easy task... why can't they make laptops with serial ports?) - worked beautifully on 1st try. A 3 day learning experience...

Click to expand...

ML1400 is Ethernet capable...