Rockwell Automation 1771-DCM USER MANUAL 1771-DCM - Manual (Page 32)

Programming the 1771-DCM
Chapter 6
6Ć11
BTR/BTW Module Address
The module address of BTR and BTW instructions in the supervisory
processor’s program is the configured address of the 1771–DCM. It is the
I/O rack number and starting module group number (its slot number is
always zero for block transfer) that you set using Switch Banks 0 and 1).
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) or (MVF)
Use this instruction to store data received from the 1771–DCM. File A
address of the FFM or MVF is the same as the BTR file address. File R
address of the FFM or MVF is a storage file for data from the
1771–DCM.
Your ladder program for the supervisory processor 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 ladder program does not use this word for any other
purpose.