Micrologix 1100 String Manipulation & Addressing

Hello,

This is my first post on this forum. There are a lot of smart people on here and I hope that one of them can answer my question.

What I am trying to do is very simple and thus my frustration. The plc that I am using is a Micrologix 1100. I have a table of 50 messages located in ST9:0 through ST9:49. The number of the fault message is located in N7:4. Life would be easy is the AWT (Ascii WriTe instruction) would let me do someing such as use ST9:[N7:4] as the source, but that instruction does not allow the use of indirect addresses, only direct addresses.

I thought of using indexed addressing by first moving N7:4 into S:24 and then using the COPY instruction with #ST9:0 as the source and place the result in ST9:50, but the ML1100 requires that the same type of addressing be used for the source and destination. (The AWT could have always used ST9:50 as the source.)

Am I going to be forced to duplicate 50 rungs of AWT instructions or is there a simple cure for my problem?

Why don't you use the COP instruction (run every scan) to move the active message ST9:[N7:4] into another string register, say ST9:50. Then you can directly address ST9:50 in your AWT instruction. I am pretty sure you can use indirect addressing in a COP.

I tried that but got the following message: ERROR Element level indirection is not supported.

It did not let me do the following on the copy instruction:
Source: ST9:[N7:4]
Destination: ST9:50

It always threw in the indexed indicator # in front of the source and destination when doing this and looked like this:
Source: #ST9:[N7:4]
Destination: #ST9:50

Which then gave me that error.

Thanks for the help.

I'm somewhat new to Allen Bradley and I can't believe how lame some of the programming and memory limitations truly are.

you might try to add 50 rungs of logic to manipulate your string file.

if the message = x, then manipulate your message.

i know its long and drawn out, but if that's what is takes,

regards,
james

"you might try to add 50 rungs of logic to manipulate your string file."

That is what I ended up doing. It is pretty sad that the ML1100, a fairly new plc, does not more flexible methods for addressing string data - AB has no excuse for that.

I have done what you're trying to do with indirect addressing in the past but only with SLC processors. I just read in the RSLogix help that indirect addressing is only supported on the SLC and ML1500 processors--that was news to me.

Electrically_Bound said:

I'm somewhat new to Allen Bradley and I can't believe how lame some of the programming and memory limitations truly are.

Click to expand...

You'll get used to it. I've never run into a situation where I couldn't do something that I wanted to with an AB PLC. Granted, I am often looking for workarounds but I usually find them.

Electrically_Bound said:

AB has no excuse for that

Click to expand...

Sure they do, it's called market share.

kolyur said:

I have done what you're trying to do with indirect addressing in the past but only with SLC processors. I just read in the RSLogix help that indirect addressing is only supported on the SLC and ML1500 processors--that was news to me.



You'll get used to it. I've never run into a situation where I couldn't do something that I wanted to with an AB PLC. Granted, I am often looking for workarounds but I usually find them.



Sure they do, it's called market share.

Click to expand...

Your right, AB is the 800 pound gorilla when it comes to the US plc market.

AB sort of reminds me of Microsoft. They were both fortunate to get their feet in early and gain market share. They got big because they were early, not neccessarily because they were good.

Anyway I got the program roughed in to do the communication and believe that I have a wiring issue between the m1100 and the LED message display, but before I can get back to work on that, I have been told to drop that and work on a different project.