Channel 0

[Guest trn_psycho]

Anyone ever used the escape keys to return a port to system mode from user mode? What I mean is, I've changed my channel 0 over from system to user/ascii, but would like to know how to send the command that will change the port back if needed. (I'm on a slc 503. The DH-485 port already has a panel view on it and that's where I'd normally hook up. The problem is, none of our maintenance guys seem to understand that and they keep calling me out to look at "A troublesome serial port." No matter how many times I explain it to them, they just seem to like using the serial connection. They have rslogix 6.something pro installed, so if I have to do it via a vba call, it's not a problem. I've just never seen it done... Any Ideas?

[Guest]

Greetings, see if this helps ... first make sure that the “Mode Change Enabled” box is checked ON ... note that the “Mode Attention Character” has the default value “\1b” which is the “Escape” key ... the “System Mode Character” has the default value of “S” ... note that this is a “CAPITAL” letter ... now start up Microsoft HyperTerminal and set up the connection for the proper baud rate, etc. to match your SLC’s Channel 0 setup ... hit the “Escape” key ... and then the “S” key (note that it’s a CAPITAL) ... if you’re lucky, the SLC’s Channel 0 should revert from being an ASCII (User Mode) port to being a programming (System Mode) port again ... now disconnect HyperTerminal and start up RSLogix500/RSLinx to go “online” with the SLC through Channel 0 ... once you’re through with your programming, etc. stay “online” and go to the screen shown below ... manually switch the “Mode” from “System” to back to “User” ... survival tip: be sure to have your maintenance crew experiment with this procedure SEVERAL times before trying it on a real-world application ... for some reason, most people seem to have a problem doing this particular operation ... especially if they need it only once in a blue moon ... maybe it’s having to use HyperTerminal? ... disclaimer: this is written from memory and it’s been at least a year or two since I’ve done this ... I apologize in advance if I’ve dropped a stitch or two ... let me know if it doesn’t work ... I’ll set up a system in the lab and work through it for you ... best regards, Ron

[Ken Roach 194]

Here's a method I always wanted to try.... wire up a DB-9 plug to jumper Tx to Rx, and put it in the enclosure for circumstances like this. Program a button somewhere else in the enclosure (maybe on the PanelView?) to trigger an AWT instruction to send "\1bS" out the serial port. If the SLC sees the string it just sent (because of the jumper), maybe it will switch back to System Mode. I have not tried this, but it seems like it would be a neat workaround. Edited 8 Feb 2005 by Ken Roach

[Guest trn_psycho]

Thanks for the replies... For now, I'll use the hyperterminal suggestion. I'm VERY intrested in the other "trick" though to see if it would work. Anyone ever tried this?

[Guest]

Greetings to all, good news ... the brilliant idea proposed by my distinguished colleague, Ken Roach, works perfectly ... if anyone has any questions about the experiments I ran, I will try to answer them ... but I think that the screen shot below should be self-explanatory ... thanks, Ken ... this one will definitely go into my little black book of “neat tricks” ... best regards, Ron Edited 8 Feb 2005 by Ron Beaufort

[Guest trn_psycho]

Now I must say, that's a slick (er... lets call it SLC) idea. Works great to. Thanks Ken. (You can never have to many tricks in your bag.)

[Guest Guest]

Would it be possible to do this same thing and set channel 0 back to "User" mode?

[Guest]

I’ll try it out in a day or two and let you know ... but the reason I didn’t try it in the first place is: “why would you want to do that?” ... specifically, if you’ve got the SLC in the SYSTEM (programming mode), then presumably you should be able to go “online” with the processor ... so once you’re in there, it’s a simple matter to manually change Channel 0 back to USER (ASCII mode) right from the “Channel Configuration” screen ... but give me a day or two and I’ll give it a shot ... best regards, Ron

[Guest Guest]

From what I see in the channel configuration screen if you use "1bU" this will set the channel back to user mode. I can see a benefit to this especially if your maintenance people aren't very familiar with the channel configuration you could have a button on a panelview to change to "programming" mode and another button to change to "printer/barcode reader/whatever" mode.

[Guest trn_psycho]

I don't think the change back function will work. Haven't tried it yet, but considering the port will no longer be in ascii mode, it shouldn't even read the switch back command. (I could be wrong though...)

[Guest]

I'm thinking that it will be able to "read" the "switch-over" command ... or else why would there even be a command available for this particular operation? ... but ... I'm thinking that it won't be able to use the AWT instruction to "send" the "switch-over" command ... since the channel won't be in ASCII mode ... my best bet so far is that HyperTerminal will work ... but the "foldback" connector trick won't ... but I'm not betting anything more than pocket change ... I should know for sure by tomorrow afternoon ... too busy with manual labor until then ... best regards, Ron

[Guest]

Greetings to all, OK ... I tried it and as far as I can tell, it won't work ... I can switch back and forth (in either direction) between System mode and User mode using HyperTerminal with no problem ... and I can use Ken's "foldback" method to switch from User mode to System mode with no problem ... but nothing that I've tried (and I've tried a LOT) will allow me to use the "foldback" method to switch from System mode to User mode ... actually I don't see this as a big disadvantage ... as I said in an earlier post, once the System mode has been established, then it should be possible to go online with the processor and make the switch back to User mode from the Channel Configuration screen ... best regards, Ron

[Guest trn_psycho]

Hmmm... On that note, is there a way (hyperteminal maybe) to hook up to the ASCII enabled port and read the data comming out of it.

[Guest]

sure ... we do that quite often when we're setting up Channel 0 to "talk" to various serial port devices ... the basic idea is to confirm that the correct characters are being transmitted - at the correct time - before connecting the actual serial device ... it gets a little bit tricky when the output happens to be "unprintable" ASCII characters - but there are "monitoring" software packages available that make this possible too ... we can also use HyperTerminal to transmit into the Channel 0 port for similar reasons ... this lets us temporarily eliminate something like a barcode reader, etc. for testing purposes ... this gives us complete control over what - and when - gets sent into the PLC's serial port ... going one step further ... with a little bit of imaginative wiring, it's completely possible to hook up an extra computer to "eavesdrop" on the serial line ... using this approach and a good monitoring software package will often reveal some interesting and highly useful information about how various devices communicate with each other over the serial link ... sometimes this is the most effective way to troubleshoot these types of systems when things don't seem to work just right ... best regards, Ron