Rockwell Automation 1785-Lx0C15 ControlNet PLC-5 Programmable Controllers User Manual - Manual (Page 57)

1785-UM022C-EN-P - February 2008
Planning to Use Your ControlNet PLC-5 Processor 2-19
Discrete I/O Data-Transfer Mapping
Regardless of the type of I/O—e.g., 1747, 1771, 1794—all
ControlNet discrete I/O data is stored within the processor according
to the corresponding I/O map-table entry. Discrete I/O data can be
stored in either the I/O image table or the DIF/DOF. Any status
information transferred along with the I/O data is stored in a separate
status file that you specify during configuration.
Important: If you want to force your discrete I/O, you must map it
to the I/O image table.
Non-discrete I/O Data-Transfer Mapping
ControlNet non-discrete I/O data can be stored in either the I/O image
table or the DIF/DOF. The ControlNet processor supports two distinct
image files; both are integer data-table files that you specify:
• Data Input File (DIF)
• Data Output File (DOF)
Each map-table entry for a non-discrete I/O data transfer defines an
offset into the DIF or DOF where the data is stored. Using separate
data-table files for non-discrete I/O data transfer allows the processor
to scan non-discrete I/O data asynchronously to the program scan.
Like discrete I/O, the data is presented synchronously to the processor
and output buffers during housekeeping.
The DIF and DOF can be overlapped (as in Figure 2.1) so that inputs
from one device can be used as outputs to another device. As a result
of the overlap, no ladder logic is required to copy the data. If either
the DIF or DOF size is greater than 1000 words, then it will span
multiple physical files. The physical files comprising the DIF or DOF
must be contiguous.
Figure 2.1 Data Input and Data Output Files
N10:0
N10:999
DIF
DOF
N11:249
N11:0
N11:499