Micrologix file copy instruction

[motor-mike]

I am trying to program my own stack so I can handle it my own way rather than using the built in stack instructions (hum, I just had an idea). I am using an AB Micrologix 1200 Series C controller and am having problems with the cop (copy file) instruction as it acts like the file fill instruction, filling the dest location with length copies of the singular source location. This is not how I read the documentation for this instruction.

Am I crazy, or is there a problem.

Thanks

 

[Doug-P]

I'll go out on a limb here and guess that what you've got is something like:

              COP

              +---------+

---| |--------| N12:0   |  (source)

              | N12:1   |  (destn)

              | LEN 10  | 

              +---------+

If this is true, what is happening is that N12:0 gets copied to N12:1, then N12:1 gets copied to N12:2, etc. Whatever was in N12:0 gets propagated through the entire file (stack).

My suggestion to get around this would be to copy to a 'scratchpad file' and then back to the main file in order to do the PUSHing. The logic outline below will PUSH a word onto the stack:

The main file is copied to the scratchpad 

              COP

              +---------+

---| |--------| N12:0   |  (main)

              | N13:0   |  (scratch)

              | LEN 9   | 

              +---------+

The scratchpad file is copied back to the main file shifted up by one word

              COP

              +---------+

---| |--------| N13:0   |  (scratch)

              | N12:1   |  (main)

              | LEN 9   | 

              +---------+

The incoming word is copied to the main file in the first position

              MOV

              +---------+

---| |--------| N7:0    |

              | N12:0   |

              +---------+ 

POPping is a lot easier, MOV the word being popped to wherever you need it and then do a COP this way:

              COP

              +---------+

---| |--------| N12:1   |  (main)

              | N12:0   |  (main)

              | LEN 9   | 

              +---------+

 

[motor-mike]

Doh!

You are completely right.

I didn't even need to finish reading, but thank you on the scratch file suggestion as it is exactly what I need.

Having spent the past 6 years programming in C++ it would have taken me a while to remember to look back to my assembly language days when programming a PLC. Now that my higher level programming paradigm has been properly reset I think I can manage it from here.

 

[Doug-P]

Doh!

We all need a little memory jog now and then!