RSLogix File Command Question

So if I see the command:

              ______________

    --------- | COP          |----

             |              |

              | Source #N7:0 |

             | Dest  #F8:20 |

             | Length    20  |

               --------------   

     

That means that:
the data in N7:0 will be loaded and converted to real and stored in F8:20,
the data in N7:1 will be loaded and converted to real and stored in F8:21,
the data in N7:2 will be loaded and converted to real and stored in F8:22,
.
.
.
the data in N7:19 will be loaded and converted to real and stored in F8:39.

Right?

(The # indicates the starting address for the operation and length is the number of elements. Correct? )

Do the SLCs automatically convert between number formats when using different types in MOV and COP commands?

Yes.
You've got it exactly.

The AB copy command (COP) is a direct byte-for-byte transfer. It WILL NOT perform type conversion.

So in the original example:

N7:0 and N7:1 will be copied into F8:20
N7:2 and N7:3 will be copied into F8:21
N7:4 and N7:5 will be copied into F8:22
.
.
.
N7:38 and N7:38 will be copied into F8:39

Two things to keep in mind. The first is that this is a direct byte for byte copy. The numbers in N7:0 and N7:1, for example, won't look anything what will end up in F8:20. The second thing is that the COP instruction length is in units of the detination data type. So the '20' in this case is 20 floating point values, which is the same quantity of bytes as 40 integers.

This type of thing is often done to get around data transfer limitations on some devices. For example, if your data transport mechanism only supports transferring integers but you need to transfer a float, you can copy a float into two successive integers, transfer them, then copy the integers back to a float to get the value back.

A MOV instruction is different. That instruction WILl do do data type conversions for you if it can.

Keith

As Kamenges said, it's an exact copy, no conversion.

Sorry for any confusion, I answered pre edit.

Hans,

Since you are copying from a 16 bit word to a float without conversion, it may be helpful for you to view this tehcnote to understand how floating point numbers are stored.

http://domino.automation.rockwell.com/applications/kb/RAKB.nsf/0/85C2838CBFC456D285256AFB00695031?OpenDocument

I linked to a really useful tool to see how floating point numbers are stored here in this thread: http://www.plctalk.net/qanda/showthread.php?t=20575
http://domino.automation.rockwell.c...85C2838CBFC456D285256AFB00695031?OpenDocument

To amplify on Kamenges reply the type of the destination defines the number of items copied from the source. If the target was a timer then three words are copied for each item. So a copy from N7 to T4 of 20 items would actually copy 30 N registers. Or at least ry to. But as noted befor, it's a straight copy with no conversions.

keith,

in ur reply u said that

N7:0 and N7:1 will be copied into F8:20
N7:2 and N7:3 will be copied into F8:21
N7:4 and N7:5 will be copied into F8:22
.
.
.
N7:38 and N7:38 will be copied into F8:39

Click to expand...

N7:38 and N7:38 will be copied into F8:39....so the same value is repeated???

please clarify

Thanks

MiamiEngineer said:

keith,

in ur reply u said that



N7:38 and N7:38 will be copied into F8:39....so the same value is repeated???

please clarify

Thanks

Click to expand...

I expect that is a typo.

It should say:
N7:38 and N7:39 will be copied into F8:39