Rockwell Automation 1771-DCM USER MANUAL 1771-DCM - Manual (Page 23)

Programming the 1771-DCM
Chapter 6
6Ć2
Block Transfer and File Move Instructions
Enter these instructions using the following information:
BTR/BTW Module Address
The module address of BTR and BTW instructions in the local
processor’s program is the physical location of the 1771–DCM. It is the
I/O rack, module group, and slot number (RGS) of the 1771–DCM:
In the same I/O chassis with the local processor
In an I/O chassis connected to a processor configured for local or
remote I/O operation
Block Length/File Length
Generally, set them to the number of words that you set for the
1771–DCM. If you have reason to set the read block length different
from the write block length (PLC–2 family processors), be sure that both
the BTR and BTW instructions cannot be enabled in the same scan.
When moving or transferring words into the BTW file for transfer to the
1771–DCM, be sure to avoid placing data in the first word because the
1771–DCM inserts status in this word.
File–to–File Move (FFM)
Use this instruction to store data received from the 1771–DCM. File A
address of the FFM is the same as the BTR file address. File R address is
a storage file for data received from the 1771–DCM.
Your ladder program must place data into the BTW file for transfer to the
1771–DCM. We leave this ladder logic to you because your application
and processor’s set of instructions determine how you would do this.
Examine the status word received from the 1771–DCM as a condition for
using the read block transfer data. Zero the status word at power–up and
be sure that your program does not use this word for any other purpose.