Micrologix 1200 PLC Memory / Data Files

[mike64b]

So I'm working on writing my first PLC program, and I don't really understand the PLC memory / data files. I see the various things like Integer, Floating Point, etc data registers but as far as choosing which of those to use, are they all available? I think maybe I'm in need of a good readup of using /storing values in memory, can anyone recommend a good site that details this?

 

[mike64b]

I was going to edit the first post but I don't see an edit button.. anyways:

I should be more specific. Firstly, I see sample programs that have N7:0 .. is this a 16bit register used for storing integers? If so, there are multiples i'm assuming? like N7:1, N7:2, etc that each store 16bit integers?

Next, i've read a bit about direct and immediate addressing but I still don't realy understand it.

For example, if I use a MOV instruction

I do:
MOV
Source 0
?
Dest N7:2
?

Is this direct addressing? And also what are the question marks indicating? When I look at some sample programs instead of the question marks on those lines they have 0< but the field is non-editable for me..

Thanks!

 

[Ken Roach]

Well, you're looking at it. The "Learn PLCs" section of PLCTalk.net is vendor-neutral but eventually most tutorials get into the Allen-Bradley SLC/PLC memory syntax.

Let me throw a few more things at you. First, online:

1. LogixPro simulator, from www.TheLearningPit.com. Their "Get Started" page loops around and recommends this site, and Phil Melore's book.

http://thelearningpit.com/plc/plcs.html

2. Professor Hugh Jack's textbook, Automated Manufacturing Systems. Available for download for free:

http://forums.mrplc.com/index.php?autocom=downloads&showfile=156

3. The MicroLogix 1200 & 1500 Instruction Set Reference Manual:

http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1762-rm001_-en-p.pdf

Chapter 2 describes Controller Memory and File Types in detail, with specifics for your MicroLogix 1200 controller.

 

[Ken Roach]

Here on the Forum the [Edit] button stays available for a few minutes to allow you to fix errors, add details, or think better of the name you just called somebody.

The default Signed Integer data file is N7. The file can be between 1 and 255 elements long, and generally it expands automatically when you use new elements in the program.

All integers in the A-B world are signed, and all addressing begins at zero.

So a 16-bit Integer has 15 data bits, and the highest bit (bit number 15) is the Sign bit. The value range is -32768 to +32767.

What you're seeing with the question marks is just RSLogix 500 not showing you the value of a register inline with the instruction until the program is compiled. Don't sweat it.


The SLC/MicroLogix operating system supports constants, data file registers and both Indexed and Indirect addressing. Stick with ordinary direct addressing to start with, where you designate the Data File Type, the Data File Element, and sometimes the Data File Sub-Element.

"N7:1" tells the operating system you're referring to an Integer data file, file 7, word 1.

"N7:1/2" tells the operating system you're referring to an Integer data file, file 7, word 1, bit 02.

 

[mike64b]

Thanks for the replies. Now when a program has say COP instruction with;
Source #N9:20
DEST #O:1.0
Length 8

I go look at the data files and look at N9, and see Offset N9:20 and it has 10 columns labeled from 0 to 9. I'm assuming that the COP instruction means to move N9:20, N9:21, etc all the way to N9:27 into O:1.0 up to O:1.7 ?

Is the # sign just there to indicate the group of data file registers?

 

[Mickey]

See below for an addressing manual for the PLC5. ( disregard the "Logical Address Identifier" $) The rest is valid.

The # sign is a pointer, ( points to the first word)